HHH-16441 - Improve support for @BatchSize

HHH-16466 - ARRAY parameter support for multi-key loads
HHH-16509 - Split parameter limit and IN element limit

(cherry picked from commit 25a23fd1c0)

README.adoc

@@ -204,3 +204,19 @@ The following table illustrates a list of commands for various databases that ca
 |`./docker_db.sh cockroachdb`
 |`./gradlew test -Pdb=cockroachdb`
 |===
+
+To stop a container started by `docker`, use the command
+
+[source]
+----
+docker stop $container_name
+----
+
+NOTE:: Substitute `podman` command for `docker` if using `podman`
+
+E.g., to stop the mariadb container
+
+[source]
+----
+docker stop mariadb
+----

hibernate-core/src/main/java/org/hibernate/dialect/DerbyDialect.java

@@ -628,6 +628,14 @@ public class DerbyDialect extends Dialect {
 		return false;
 	}
 
+	@Override
+	public int getInExpressionCountLimit() {
+		// Derby does not have a limit on the number of expressions/parameters per-se (it may, I just
+		// don't know). It does, however, have a limit on the size of the SQL text it will accept as a
+		// PreparedStatement; so let's limit this to a sensible value to avoid that.
+		return 512;
+	}
+
 	@Override
 	public SQLExceptionConversionDelegate buildSQLExceptionConversionDelegate() {
 		return (sqlException, message, sql) -> {

hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java

@@ -109,7 +109,7 @@ import org.hibernate.internal.util.MathHelper;
 import org.hibernate.internal.util.StringHelper;
 import org.hibernate.internal.util.collections.ArrayHelper;
 import org.hibernate.internal.util.io.StreamCopier;
-import org.hibernate.loader.BatchLoadSizingStrategy;
+import org.hibernate.loader.ast.spi.MultiKeyLoadSizingStrategy;
 import org.hibernate.mapping.Column;
 import org.hibernate.mapping.Constraint;
 import org.hibernate.mapping.ForeignKey;
@@ -178,9 +178,6 @@ import org.hibernate.type.descriptor.java.PrimitiveByteArrayJavaType;
 import org.hibernate.type.descriptor.jdbc.ArrayJdbcType;
 import org.hibernate.type.descriptor.jdbc.BlobJdbcType;
 import org.hibernate.type.descriptor.jdbc.ClobJdbcType;
-import org.hibernate.type.descriptor.jdbc.TimeUtcAsOffsetTimeJdbcType;
-import org.hibernate.type.descriptor.jdbc.TimestampUtcAsJdbcTimestampJdbcType;
-import org.hibernate.type.descriptor.jdbc.TimestampUtcAsOffsetDateTimeJdbcType;
 import org.hibernate.type.descriptor.jdbc.JdbcLiteralFormatter;
 import org.hibernate.type.descriptor.jdbc.JdbcType;
 import org.hibernate.type.descriptor.jdbc.LongNVarcharJdbcType;
@@ -188,6 +185,9 @@ import org.hibernate.type.descriptor.jdbc.NCharJdbcType;
 import org.hibernate.type.descriptor.jdbc.NClobJdbcType;
 import org.hibernate.type.descriptor.jdbc.NVarcharJdbcType;
 import org.hibernate.type.descriptor.jdbc.TimeUtcAsJdbcTimeJdbcType;
+import org.hibernate.type.descriptor.jdbc.TimeUtcAsOffsetTimeJdbcType;
+import org.hibernate.type.descriptor.jdbc.TimestampUtcAsJdbcTimestampJdbcType;
+import org.hibernate.type.descriptor.jdbc.TimestampUtcAsOffsetDateTimeJdbcType;
 import org.hibernate.type.descriptor.jdbc.spi.JdbcTypeRegistry;
 import org.hibernate.type.descriptor.sql.internal.CapacityDependentDdlType;
 import org.hibernate.type.descriptor.sql.internal.DdlTypeImpl;
@@ -3797,6 +3797,18 @@ public abstract class Dialect implements ConversionContext, TypeContributor, Fun
 		return 0;
 	}
 
+	/**
+	 * Return the limit that the underlying database places on the number of parameters
+	 * that can be defined for a PreparedStatement.  If the database defines no such
+	 * limits, simply return zero or a number smaller than zero.  By default, Dialect
+	 * returns the same value as {@link #getInExpressionCountLimit()}.
+	 *
+	 * @return The limit, or a non-positive integer to indicate no limit.
+	 */
+	public int getParameterCountLimit() {
+		return getInExpressionCountLimit();
+	}
+
 	/**
 	 * Must LOB values occur last in inserts and updates?
 	 *
@@ -4031,41 +4043,44 @@ public abstract class Dialect implements ConversionContext, TypeContributor, Fun
 		return null;
 	}
 
-	protected final BatchLoadSizingStrategy STANDARD_DEFAULT_BATCH_LOAD_SIZING_STRATEGY =
+	/**
-			(numberOfKeyColumns, numberOfKeys, inClauseParameterPaddingEnabled) -> {
+	 * The strategy used to determine the appropriate number of keys
-		final int paddedSize;
+	 * to load in a single SQL query with multi-key loading.
-
+	 * @see org.hibernate.Session#byMultipleIds
-		if ( inClauseParameterPaddingEnabled ) {
+	 * @see org.hibernate.Session#byMultipleNaturalId
-			paddedSize = MathHelper.ceilingPowerOfTwo( numberOfKeys );
+	 */
-		}
+	public MultiKeyLoadSizingStrategy getMultiKeyLoadSizingStrategy() {
-		else {
+		return STANDARD_MULTI_KEY_LOAD_SIZING_STRATEGY;
-			paddedSize = numberOfKeys;
+	}
-		}
-
-		// For tuples, there is no limit, so we can just use the power of two padding approach
-		if ( numberOfKeyColumns > 1 ) {
-			return paddedSize;
-		}
-		final int inExpressionCountLimit = getInExpressionCountLimit();
-		if ( inExpressionCountLimit > 0 ) {
-			if ( paddedSize < inExpressionCountLimit ) {
-				return paddedSize;
-			}
-			else if ( numberOfKeys < inExpressionCountLimit ) {
-				return numberOfKeys;
-			}
-			return getInExpressionCountLimit();
-		}
-		return paddedSize;
-	};
 
 	/**
-	 * The strategy to use for determining batch sizes in batch loading.
+	 * The strategy used to determine the appropriate number of keys
+	 * to load in a single SQL query with batch-fetch loading.
+	 *
+	 * @implNote By default, the same as {@linkplain #getMultiKeyLoadSizingStrategy}
+	 *
+	 * @see org.hibernate.annotations.BatchSize
 	 */
-	public BatchLoadSizingStrategy getDefaultBatchLoadSizingStrategy() {
+	public MultiKeyLoadSizingStrategy getBatchLoadSizingStrategy() {
-		return STANDARD_DEFAULT_BATCH_LOAD_SIZING_STRATEGY;
+		return getMultiKeyLoadSizingStrategy();
 	}
 
+	protected final MultiKeyLoadSizingStrategy STANDARD_MULTI_KEY_LOAD_SIZING_STRATEGY = (numberOfColumns, numberOfKeys, pad) -> {
+		numberOfKeys = pad ? MathHelper.ceilingPowerOfTwo( numberOfKeys ) : numberOfKeys;
+
+		final long parameterCount = (long) numberOfColumns * numberOfKeys;
+		final int limit = getParameterCountLimit();
+
+		if ( limit > 0 ) {
+			// the Dialect reported a limit -  see if the parameter count exceeds the limit
+			if ( parameterCount >= limit ) {
+				return limit / numberOfColumns;
+			}
+		}
+
+		return numberOfKeys;
+	};
+
 	/**
 	 * Is JDBC statement warning logging enabled by default?
 	 *

hibernate-core/src/main/java/org/hibernate/dialect/DialectDelegateWrapper.java

@@ -47,7 +47,7 @@ import org.hibernate.engine.jdbc.env.spi.SchemaNameResolver;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.exception.spi.SQLExceptionConversionDelegate;
 import org.hibernate.exception.spi.ViolatedConstraintNameExtractor;
-import org.hibernate.loader.BatchLoadSizingStrategy;
+import org.hibernate.loader.ast.spi.MultiKeyLoadSizingStrategy;
 import org.hibernate.mapping.Column;
 import org.hibernate.mapping.Constraint;
 import org.hibernate.mapping.ForeignKey;
@@ -90,7 +90,6 @@ import org.hibernate.type.descriptor.jdbc.JdbcType;
 import org.hibernate.type.descriptor.jdbc.spi.JdbcTypeRegistry;
 import org.hibernate.type.spi.TypeConfiguration;
 
-import jakarta.persistence.GenerationType;
 import jakarta.persistence.TemporalType;
 
 /**
@@ -1161,6 +1160,11 @@ public class DialectDelegateWrapper extends Dialect {
 		return wrapped.getInExpressionCountLimit();
 	}
 
+	@Override
+	public int getParameterCountLimit() {
+		return wrapped.getParameterCountLimit();
+	}
+
 	@Override
 	public boolean forceLobAsLastValue() {
 		return wrapped.forceLobAsLastValue();
@@ -1247,8 +1251,13 @@ public class DialectDelegateWrapper extends Dialect {
 	}
 
 	@Override
-	public BatchLoadSizingStrategy getDefaultBatchLoadSizingStrategy() {
+	public MultiKeyLoadSizingStrategy getBatchLoadSizingStrategy() {
-		return wrapped.getDefaultBatchLoadSizingStrategy();
+		return wrapped.getBatchLoadSizingStrategy();
+	}
+
+	@Override
+	public MultiKeyLoadSizingStrategy getMultiKeyLoadSizingStrategy() {
+		return wrapped.getMultiKeyLoadSizingStrategy();
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/dialect/HSQLSqlAstTranslator.java

@@ -25,6 +25,7 @@ import org.hibernate.sql.ast.tree.expression.Literal;
 import org.hibernate.sql.ast.tree.expression.SqlTuple;
 import org.hibernate.sql.ast.tree.expression.Summarization;
 import org.hibernate.sql.ast.tree.predicate.BooleanExpressionPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.select.QueryPart;
 import org.hibernate.sql.exec.spi.JdbcOperation;
 import org.hibernate.type.descriptor.jdbc.ArrayJdbcType;
@@ -57,6 +58,15 @@ public class HSQLSqlAstTranslator<T extends JdbcOperation> extends AbstractSqlAs
 		}
 	}
 
+	@Override
+	public void visitInArrayPredicate(InArrayPredicate inArrayPredicate) {
+		// column in ( unnest(?) )
+		inArrayPredicate.getTestExpression().accept( this );
+		appendSql( " in (unnest(" );
+		inArrayPredicate.getArrayParameter().accept( this );
+		appendSql( "))" );
+	}
+
 	@Override
 	protected boolean supportsArrayConstructor() {
 		return true;

hibernate-core/src/main/java/org/hibernate/dialect/PostgreSQLSqlAstTranslator.java

@@ -18,6 +18,7 @@ import org.hibernate.sql.ast.tree.expression.Expression;
 import org.hibernate.sql.ast.tree.expression.Literal;
 import org.hibernate.sql.ast.tree.expression.Summarization;
 import org.hibernate.sql.ast.tree.predicate.BooleanExpressionPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.LikePredicate;
 import org.hibernate.sql.ast.tree.predicate.NullnessPredicate;
 import org.hibernate.sql.ast.tree.select.QueryGroup;
@@ -38,6 +39,19 @@ public class PostgreSQLSqlAstTranslator<T extends JdbcOperation> extends SqlAstT
 		super( sessionFactory, statement );
 	}
 
+	@Override
+	public void visitInArrayPredicate(InArrayPredicate inArrayPredicate) {
+		inArrayPredicate.getTestExpression().accept( this );
+		appendSql( " = any (" );
+		inArrayPredicate.getArrayParameter().accept( this );
+		appendSql( ")" );
+	}
+
+	@Override
+	protected String getArrayContainsFunction() {
+		return super.getArrayContainsFunction();
+	}
+
 	@Override
 	protected void renderInsertIntoNoColumns(TableInsertStandard tableInsert) {
 		renderIntoIntoAndTable( tableInsert );

hibernate-core/src/main/java/org/hibernate/dialect/SQLServerDialect.java

@@ -118,7 +118,13 @@ import static org.hibernate.type.descriptor.DateTimeUtils.appendAsTimestampWithM
  */
 public class SQLServerDialect extends AbstractTransactSQLDialect {
 	private final static DatabaseVersion MINIMUM_VERSION = DatabaseVersion.make( 10, 0 );
-	private static final int PARAM_LIST_SIZE_LIMIT = 2100;
+
+	/**
+	 * NOTE : 2100 is the documented limit supposedly - but in my testing, sending
+	 * 2100 parameters fails saying it must be less than 2100.
+	 */
+	private static final int PARAM_LIST_SIZE_LIMIT = 2048;
+
 	// See microsoft.sql.Types.GEOMETRY
 	private static final int GEOMETRY_TYPE_CODE = -157;
 	// See microsoft.sql.Types.GEOGRAPHY

hibernate-core/src/main/java/org/hibernate/dialect/SybaseDialect.java

@@ -74,7 +74,10 @@ public class SybaseDialect extends AbstractTransactSQLDialect {
 	private static final DatabaseVersion MINIMUM_VERSION = DatabaseVersion.make( 16, 0 );
 
 	//All Sybase dialects share an IN list size limit.
-	private static final int PARAM_LIST_SIZE_LIMIT = 250000;
+	private static final int IN_LIST_SIZE_LIMIT = 250000;
+
+	private static final int PARAM_COUNT_LIMIT = 2000;
+
 	private final UniqueDelegate uniqueDelegate = new SkipNullableUniqueDelegate(this);
 
 	public SybaseDialect() {
@@ -163,7 +166,12 @@ public class SybaseDialect extends AbstractTransactSQLDialect {
 
 	@Override
 	public int getInExpressionCountLimit() {
-		return PARAM_LIST_SIZE_LIMIT;
+		return IN_LIST_SIZE_LIMIT;
+	}
+
+	@Override
+	public int getParameterCountLimit() {
+		return PARAM_COUNT_LIMIT;
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/engine/internal/BatchFetchQueueHelper.java

@@ -80,6 +80,17 @@ public class BatchFetchQueueHelper {
 		batchFetchQueue.removeBatchLoadableEntityKey( entityKey );
 	}
 
+	/**
+	 * Remove the entity key with the specified {@code id} and {@code persister} from
+	 * the batch loadable entities {@link BatchFetchQueue}.
+	 */
+	public static void removeBatchLoadableEntityKey(
+			EntityKey entityKey,
+			SharedSessionContractImplementor session) {
+		final BatchFetchQueue batchFetchQueue = session.getPersistenceContextInternal().getBatchFetchQueue();
+		batchFetchQueue.removeBatchLoadableEntityKey( entityKey );
+	}
+
 	public static void removeBatchLoadableEntityKey(
 			Object id,
 			EntityMappingType entityMappingType,

hibernate-core/src/main/java/org/hibernate/engine/profile/internal/FetchProfileAffectee.java

@@ -0,0 +1,21 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.engine.profile.internal;
+
+import org.hibernate.engine.profile.Fetch;
+
+/**
+ * Commonality between entities and collections as something that can be affected by fetch profiles.
+ *
+ * @author Steve Ebersole
+ */
+public interface FetchProfileAffectee {
+	/**
+	 * Register the profile name with the entity/collection
+	 */
+	void registerAffectingFetchProfile(String fetchProfileName, Fetch.Style fetchStyle);
+}

hibernate-core/src/main/java/org/hibernate/engine/spi/BatchFetchQueue.java

@@ -16,8 +16,11 @@ import org.hibernate.cache.spi.access.EntityDataAccess;
 import org.hibernate.collection.spi.PersistentCollection;
 import org.hibernate.engine.internal.CacheHelper;
 import org.hibernate.internal.CoreLogging;
+import org.hibernate.internal.util.IndexedConsumer;
 import org.hibernate.internal.util.collections.CollectionHelper;
+import org.hibernate.metamodel.mapping.EntityIdentifierMapping;
 import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.persister.collection.CollectionPersister;
 import org.hibernate.persister.entity.EntityPersister;
 
@@ -183,6 +186,61 @@ public class BatchFetchQueue {
 		return false;
 	}
 
+	/**
+	 * A "collector" form of {@link #getBatchLoadableEntityIds}.  Useful
+	 * in cases where we want a specially created array/container - allows
+	 * creation of concretely typed array for ARRAY param binding to ensure
+	 * the driver does not need to cast/copy the values array.
+	 */
+	public <T> void collectBatchLoadableEntityIds(
+			final int domainBatchSize,
+			IndexedConsumer<T> collector,
+			final T loadingId,
+			final EntityMappingType entityDescriptor) {
+		// make sure we load the id being loaded in the batch!
+		collector.accept( 0, loadingId );
+
+		if ( batchLoadableEntityKeys == null ) {
+			return;
+		}
+
+		final LinkedHashSet<EntityKey> set =  batchLoadableEntityKeys.get( entityDescriptor.getEntityName() );
+		if ( set == null ) {
+			return;
+		}
+
+		final EntityIdentifierMapping identifierMapping = entityDescriptor.getIdentifierMapping();
+
+		int batchPosition = 1;
+		int end = -1;
+		boolean checkForEnd = false;
+
+		for ( EntityKey key : set ) {
+			if ( checkForEnd && batchPosition == end ) {
+				// the first id found after the given id
+				return;
+			}
+
+			if ( identifierMapping.areEqual( loadingId, key.getIdentifier(), context.getSession() ) ) {
+				end = batchPosition;
+			}
+			else {
+				if ( !isCached( key, entityDescriptor.getEntityPersister() ) ) {
+					//noinspection unchecked
+					collector.accept( batchPosition++, (T) key.getIdentifier() );
+				}
+			}
+
+			if ( batchPosition == domainBatchSize ) {
+				// end of array, start filling again from start
+				batchPosition = 1;
+				if ( end != -1 ) {
+					checkForEnd = true;
+				}
+			}
+		}
+	}
+
 	/**
 	 * Get a batch of unloaded identifiers for this class, using a slightly
 	 * complex algorithm that tries to grab keys registered immediately after
@@ -292,6 +350,88 @@ public class BatchFetchQueue {
 		}
 	}
 
+
+	/**
+	 * A "collector" form of {@link #getCollectionBatch}.  Useful
+	 * in cases where we want a specially created array/container - allows
+	 * creation of concretely typed array for ARRAY param binding to ensure
+	 * the driver does not need to cast/copy the values array.
+	 */
+	public <T> void collectBatchLoadableCollectionKeys(
+			int batchSize,
+			IndexedConsumer<T> collector,
+			T keyBeingLoaded,
+			PluralAttributeMapping pluralAttributeMapping) {
+		collector.accept( 0, keyBeingLoaded );
+
+		if ( batchLoadableCollections == null ) {
+			return;
+		}
+
+		int i = 1;
+		int end = -1;
+		boolean checkForEnd = false;
+
+		final LinkedHashMap<CollectionEntry, PersistentCollection<?>> map = batchLoadableCollections.get( pluralAttributeMapping.getNavigableRole().getFullPath() );
+		if ( map == null ) {
+			return;
+		}
+
+		for ( Entry<CollectionEntry, PersistentCollection<?>> me : map.entrySet() ) {
+			final CollectionEntry ce = me.getKey();
+			final PersistentCollection<?> collection = me.getValue();
+
+			if ( ce.getLoadedKey() == null ) {
+				// the loadedKey of the collectionEntry might be null as it might have been reset to null
+				// (see for example Collections.processDereferencedCollection()
+				// and CollectionEntry.afterAction())
+				// though we clear the queue on flush, it seems like a good idea to guard
+				// against potentially null loadedKeys (which leads to various NPEs as demonstrated in HHH-7821).
+				continue;
+			}
+
+			if ( collection.wasInitialized() ) {
+				// should never happen
+				LOG.warn( "Encountered initialized collection in BatchFetchQueue, this should not happen." );
+				continue;
+			}
+
+			if ( checkForEnd && i == end ) {
+				// the first key found after the given key
+				return;
+			}
+
+			final boolean isEqual = pluralAttributeMapping.getKeyDescriptor().areEqual(
+					keyBeingLoaded,
+					ce.getLoadedKey(),
+					context.getSession()
+			);
+//			final boolean isEqual = collectionPersister.getKeyType().isEqual(
+//					id,
+//					ce.getLoadedKey(),
+//					collectionPersister.getFactory()
+//			);
+
+			if ( isEqual ) {
+				end = i;
+			}
+			else if ( !isCached( ce.getLoadedKey(), pluralAttributeMapping.getCollectionDescriptor() ) ) {
+				//noinspection unchecked
+				collector.accept( i++, (T) ce.getLoadedKey() );
+			}
+
+			if ( i == batchSize ) {
+				//end of array, start filling again from start
+				i = 1;
+				if ( end != -1 ) {
+					checkForEnd = true;
+				}
+			}
+		}
+
+		//we ran out of keys to try
+	}
+
 	/**
 	 * Get a batch of uninitialized collection keys for a given role
 	 *

hibernate-core/src/main/java/org/hibernate/internal/FetchProfileHelper.java

@@ -11,16 +11,18 @@ import org.hibernate.boot.spi.MetadataImplementor;
 import org.hibernate.engine.profile.Association;
 import org.hibernate.engine.profile.Fetch;
 import org.hibernate.engine.profile.FetchProfile;
+import org.hibernate.engine.profile.internal.FetchProfileAffectee;
 import org.hibernate.metamodel.MappingMetamodel;
+import org.hibernate.metamodel.mapping.EntityValuedModelPart;
+import org.hibernate.metamodel.mapping.ModelPart;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.persister.entity.EntityPersister;
-import org.hibernate.persister.entity.Loadable;
-import org.hibernate.type.Type;
 
 import java.util.HashMap;
 import java.util.Map;
 
 /**
- * Creates {@link FetchProfile}s.
+ * Create {@link FetchProfile} references from {@link org.hibernate.mapping.FetchProfile} references
  *
  * @author Gavin King
  */
@@ -40,28 +42,53 @@ public class FetchProfileHelper {
 	private static FetchProfile createFetchProfile(
 			MappingMetamodel mappingMetamodel,
 			org.hibernate.mapping.FetchProfile mappingProfile) {
-		final FetchProfile fetchProfile = new FetchProfile( mappingProfile.getName() );
+		final String profileName = mappingProfile.getName();
+		final FetchProfile fetchProfile = new FetchProfile( profileName );
+
 		for ( org.hibernate.mapping.FetchProfile.Fetch mappingFetch : mappingProfile.getFetches() ) {
 			// resolve the persister owning the fetch
 			final EntityPersister owner = getEntityPersister( mappingMetamodel, fetchProfile, mappingFetch );
+			( (FetchProfileAffectee) owner ).registerAffectingFetchProfile( profileName, null );
 
-			// validate the specified association fetch
+			final Association association = new Association( owner, mappingFetch.getAssociation() );
-			final Type associationType = owner.getPropertyType( mappingFetch.getAssociation() );
-			if ( associationType == null || !associationType.isAssociationType() ) {
-				throw new HibernateException( "Fetch profile [" + fetchProfile.getName()
-						+ "] specified an association that does not exist [" + mappingFetch.getAssociation() + "]" );
-			}
-
-			// resolve the style
 			final Fetch.Style fetchStyle = Fetch.Style.parse( mappingFetch.getStyle() );
 
-			// then construct the fetch instance...
+			// validate the specified association fetch
-			fetchProfile.addFetch( new Association( owner, mappingFetch.getAssociation() ), fetchStyle );
+			final ModelPart fetchablePart = owner.findByPath( association.getAssociationPath() );
-			((Loadable) owner).registerAffectingFetchProfile( fetchProfile.getName() );
+			validateFetchablePart( fetchablePart, profileName, association );
+			if ( fetchablePart instanceof FetchProfileAffectee ) {
+				( (FetchProfileAffectee) fetchablePart ).registerAffectingFetchProfile( profileName, fetchStyle );
+			}
+
+			// then register the association with the FetchProfile
+			fetchProfile.addFetch( association, fetchStyle );
 		}
 		return fetchProfile;
 	}
 
+	private static void validateFetchablePart(ModelPart fetchablePart, String profileName, Association association) {
+		if ( fetchablePart == null ) {
+			throw new HibernateException( String.format(
+					"Fetch profile [%s] specified an association that does not exist - %s",
+					profileName,
+					association.getRole()
+			) );
+		}
+
+		if ( !isAssociation( fetchablePart ) ) {
+			throw new HibernateException( String.format(
+					"Fetch profile [%s] specified an association that is not an association - %s",
+					profileName,
+					association.getRole()
+			) );
+		}
+	}
+
+	private static boolean isAssociation(ModelPart fetchablePart) {
+		return fetchablePart instanceof EntityValuedModelPart
+				|| fetchablePart instanceof PluralAttributeMapping;
+	}
+
 	private static EntityPersister getEntityPersister(
 			MappingMetamodel mappingMetamodel,
 			FetchProfile fetchProfile,

hibernate-core/src/main/java/org/hibernate/internal/util/collections/ArrayHelper.java

@@ -13,6 +13,9 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
+import java.util.SortedSet;
+import java.util.TreeSet;
 import java.util.function.Consumer;
 
 import org.hibernate.HibernateException;
@@ -286,33 +289,66 @@ public final class ArrayHelper {
 	public static final Type[] EMPTY_TYPE_ARRAY = {};
 	public static final byte[] EMPTY_BYTE_ARRAY = {};
 
-//	public static int[] getBatchSizes(int maxBatchSize) {
+	/**
-//		int batchSize = maxBatchSize;
+	 * Calculate the batch partitions needed to handle the {@code mappedBatchSize}.
-//		int n = 1;
+	 *
-//		while ( batchSize > 1 ) {
+	 * @param mappedBatchSize The {@link org.hibernate.annotations.BatchSize batch-size}.  Internally
-//			batchSize = getNextBatchSize( batchSize );
+	 * this is capped at {@code 256}
-//			n++;
+	 *
-//		}
+	 * @implNote The max batch size is capped at {@code 256}
-//		int[] result = new int[n];
+	 *
-//		batchSize = maxBatchSize;
+	 * @return The upper bound for the partitions
-//		for ( int i = 0; i < n; i++ ) {
+	 */
-//			result[i] = batchSize;
+	public static int[] calculateBatchPartitions(int mappedBatchSize) {
-//			batchSize = getNextBatchSize( batchSize );
+		final SortedSet<Integer> partitionSizes = new TreeSet<>( Integer::compareTo );
-//		}
+		int batchSize = Math.min( mappedBatchSize, 256 );
-//		return result;
+		while ( batchSize > 1 ) {
-//	}
+			partitionSizes.add( batchSize );
-//
+			batchSize = calculateNextBatchPartitionLimit( batchSize );
-//	private static int getNextBatchSize(int batchSize) {
+		}
-//		if ( batchSize <= 10 ) {
+
-//			return batchSize - 1; //allow 9,8,7,6,5,4,3,2,1
+		return ArrayHelper.toIntArray( partitionSizes );
-//		}
+	}
-//		else if ( batchSize / 2 < 10 ) {
+
-//			return 10;
+	private static int calculateNextBatchPartitionLimit(int batchSize) {
-//		}
+		if ( batchSize <= 10 ) {
-//		else {
+			return batchSize - 1; //allow 9,8,7,6,5,4,3,2,1
-//			return batchSize / 2;
+		}
-//		}
+		else if ( batchSize / 2 < 10 ) {
-//	}
+			return 10;
+		}
+		else {
+			return batchSize / 2;
+		}
+	}
+
+	public static int[] getBatchSizes(int maxBatchSize) {
+		int batchSize = maxBatchSize;
+		int n = 1;
+		while ( batchSize > 1 ) {
+			batchSize = getNextBatchSize( batchSize );
+			n++;
+		}
+		int[] result = new int[n];
+		batchSize = maxBatchSize;
+		for ( int i = 0; i < n; i++ ) {
+			result[i] = batchSize;
+			batchSize = getNextBatchSize( batchSize );
+		}
+		return result;
+	}
+
+	private static int getNextBatchSize(int batchSize) {
+		if ( batchSize <= 10 ) {
+			return batchSize - 1; //allow 9,8,7,6,5,4,3,2,1
+		}
+		else if ( batchSize / 2 < 10 ) {
+			return 10;
+		}
+		else {
+			return batchSize / 2;
+		}
+	}
 
 	private static final int SEED = 23;
 	private static final int PRIME_NUMBER = 37;
@@ -438,4 +474,9 @@ public final class ArrayHelper {
 			consumer.accept( array[ i ] );
 		}
 	}
+
+	@SuppressWarnings("unchecked")
+	public static <T> T[] newInstance(Class<T> elementType, int length) {
+		return (T[]) Array.newInstance( elementType, length );
+	}
 }

hibernate-core/src/main/java/org/hibernate/loader/BatchFetchStyle.java

@@ -7,6 +7,9 @@
 package org.hibernate.loader;
 
 import java.util.Locale;
+
+import org.hibernate.loader.ast.spi.MultiKeyLoadSizingStrategy;
+
 import org.jboss.logging.Logger;
 
 /**
@@ -16,7 +19,7 @@ import org.jboss.logging.Logger;
  *
  * @author Steve Ebersole
  *
- * @deprecated see {@link BatchLoadSizingStrategy} instead
+ * @deprecated see {@link MultiKeyLoadSizingStrategy} instead
  */
 @Deprecated(since = "6.0")
 public enum BatchFetchStyle {

hibernate-core/src/main/java/org/hibernate/loader/BatchLoadSizingStrategy.java

@@ -1,17 +0,0 @@
-/*
- * Hibernate, Relational Persistence for Idiomatic Java
- *
- * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
- * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
- */
-package org.hibernate.loader;
-
-/**
- * Strategy (pluggable) for determining an optimal size for batch loads.
- *
- * @author Steve Ebersole
- */
-@FunctionalInterface
-public interface BatchLoadSizingStrategy {
-	int determineOptimalBatchLoadSize(int numberOfKeyColumns, int numberOfKeys, boolean inClauseParameterPaddingEnabled);
-}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/AbstractCollectionBatchLoader.java

@@ -0,0 +1,96 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import org.hibernate.collection.spi.PersistentCollection;
+import org.hibernate.engine.spi.CollectionEntry;
+import org.hibernate.engine.spi.CollectionKey;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.PersistenceContext;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.loader.ast.spi.CollectionBatchLoader;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
+import org.hibernate.sql.results.internal.ResultsHelper;
+
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_DEBUG_ENABLED;
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER;
+
+/**
+ * @author Steve Ebersole
+ */
+public abstract class AbstractCollectionBatchLoader implements CollectionBatchLoader {
+	private final int domainBatchSize;
+	private final PluralAttributeMapping attributeMapping;
+	private final LoadQueryInfluencers influencers;
+	private final SessionFactoryImplementor sessionFactory;
+
+	private final int keyJdbcCount;
+
+	public AbstractCollectionBatchLoader(
+			int domainBatchSize,
+			LoadQueryInfluencers influencers,
+			PluralAttributeMapping attributeMapping,
+			SessionFactoryImplementor sessionFactory) {
+		this.domainBatchSize = domainBatchSize;
+		this.attributeMapping = attributeMapping;
+
+		this.keyJdbcCount = attributeMapping.getJdbcTypeCount();
+		this.sessionFactory = sessionFactory;
+		this.influencers = influencers;
+	}
+
+	@Override
+	public int getDomainBatchSize() {
+		return domainBatchSize;
+	}
+
+	@Override
+	public PluralAttributeMapping getLoadable() {
+		return attributeMapping;
+	}
+
+	public LoadQueryInfluencers getInfluencers() {
+		return influencers;
+	}
+
+	public SessionFactoryImplementor getSessionFactory() {
+		return sessionFactory;
+	}
+
+	public int getKeyJdbcCount() {
+		return keyJdbcCount;
+	}
+
+	protected void finishInitializingKey(
+			Object key,
+			SharedSessionContractImplementor session) {
+		if ( key == null ) {
+			return;
+		}
+
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf( "Finishing initializing batch-fetched collection : %s.%s", attributeMapping.getNavigableRole().getFullPath(), key );
+		}
+
+		final PersistenceContext persistenceContext = session.getPersistenceContext();
+		final CollectionKey collectionKey = new CollectionKey( getLoadable().getCollectionDescriptor(), key );
+		final PersistentCollection<?> collection = persistenceContext.getCollection( collectionKey );
+		if ( !collection.wasInitialized() ) {
+			final CollectionEntry entry = persistenceContext.getCollectionEntry( collection );
+			collection.initializeEmptyCollection( entry.getLoadedPersister() );
+			ResultsHelper.finalizeCollectionLoading(
+					persistenceContext,
+					entry.getLoadedPersister(),
+					collection,
+					collectionKey,
+					true
+			);
+		}
+
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/AbstractMultiIdEntityLoader.java

@@ -0,0 +1,71 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.event.spi.EventSource;
+import org.hibernate.loader.ast.spi.MultiIdEntityLoader;
+import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
+import org.hibernate.metamodel.mapping.EntityIdentifierMapping;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+
+import java.util.List;
+
+/**
+ * Base support for MultiIdEntityLoader implementations
+ *
+ * @author Steve Ebersole
+ */
+public abstract class AbstractMultiIdEntityLoader<T> implements MultiIdEntityLoader<T>, Preparable {
+	private final EntityMappingType entityDescriptor;
+	private final SessionFactoryImplementor sessionFactory;
+
+	private EntityIdentifierMapping identifierMapping;
+
+	public AbstractMultiIdEntityLoader(EntityMappingType entityDescriptor, SessionFactoryImplementor sessionFactory) {
+		this.entityDescriptor = entityDescriptor;
+		this.sessionFactory = sessionFactory;
+	}
+
+	@Override
+	public void prepare() {
+		identifierMapping = getLoadable().getIdentifierMapping();
+	}
+
+	protected EntityMappingType getEntityDescriptor() {
+		return entityDescriptor;
+	}
+
+	protected SessionFactoryImplementor getSessionFactory() {
+		return sessionFactory;
+	}
+
+	public EntityIdentifierMapping getIdentifierMapping() {
+		return identifierMapping;
+	}
+
+	@Override
+	public EntityMappingType getLoadable() {
+		return getEntityDescriptor();
+	}
+
+	@Override
+	public final <K> List<T> load(K[] ids, MultiIdLoadOptions loadOptions, EventSource session) {
+		assert ids != null;
+		if ( loadOptions.isOrderReturnEnabled() ) {
+			return performOrderedMultiLoad( ids, loadOptions, session );
+		}
+		else {
+			return performUnorderedMultiLoad( ids, loadOptions, session );
+		}
+	}
+
+	protected abstract <K> List<T> performOrderedMultiLoad(K[] ids, MultiIdLoadOptions loadOptions, EventSource session);
+
+	protected abstract <K> List<T> performUnorderedMultiLoad(K[] ids, MultiIdLoadOptions loadOptions, EventSource session);
+
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/BatchLoaderFactoryInitiator.java

@@ -0,0 +1,35 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.util.Map;
+
+import org.hibernate.boot.registry.StandardServiceInitiator;
+import org.hibernate.loader.ast.spi.BatchLoaderFactory;
+import org.hibernate.service.spi.ServiceRegistryImplementor;
+
+/**
+ * Initiator for {@link StandardBatchLoaderFactory}
+ *
+ * @author Steve Ebersole
+ */
+public class BatchLoaderFactoryInitiator implements StandardServiceInitiator<BatchLoaderFactory> {
+	/**
+	 * Singleton access
+	 */
+	public static final BatchLoaderFactoryInitiator INSTANCE = new BatchLoaderFactoryInitiator();
+
+	@Override
+	public BatchLoaderFactory initiateService(Map<String, Object> configurationValues, ServiceRegistryImplementor registry) {
+		return new StandardBatchLoaderFactory( configurationValues, registry );
+	}
+
+	@Override
+	public Class<BatchLoaderFactory> getServiceInitiated() {
+		return BatchLoaderFactory.class;
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/CacheEntityLoaderHelper.java

@@ -104,6 +104,32 @@ public class CacheEntityLoaderHelper {
 		return new PersistenceContextEntry( old, EntityStatus.MANAGED );
 	}
 
+	/**
+	 * Attempts to locate the entity in the session-level cache.
+	 * <p>
+	 * If allowed to return nulls, then if the entity happens to be found in
+	 * the session cache, we check the entity type for proper handling
+	 * of entity hierarchies.
+	 * <p>
+	 * If checkDeleted was set to true, then if the entity is found in the
+	 * session-level cache, its current status within the session cache
+	 * is checked to see if it has previously been scheduled for deletion.
+	 *
+	 * @param event The load event
+	 * @param keyToLoad The EntityKey representing the entity to be loaded.
+	 * @param options The load options.
+	 *
+	 * @return The entity from the session-level cache, or null.
+	 *
+	 * @throws HibernateException Generally indicates problems applying a lock-mode.
+	 */
+	public static PersistenceContextEntry loadFromSessionCacheStatic(
+			final LoadEvent event,
+			final EntityKey keyToLoad,
+			final LoadEventListener.LoadType options) {
+		return INSTANCE.loadFromSessionCache( event, keyToLoad, options );
+	}
+
 	/**
 	 * Attempts to locate the entity in the session-level cache.
 	 * <p>

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/CollectionBatchLoaderArrayParam.java

@@ -0,0 +1,163 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.lang.reflect.Array;
+import java.util.Collections;
+
+import org.hibernate.LockOptions;
+import org.hibernate.collection.spi.PersistentCollection;
+import org.hibernate.engine.spi.CollectionKey;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.engine.spi.SubselectFetch;
+import org.hibernate.loader.ast.spi.CollectionBatchLoader;
+import org.hibernate.loader.ast.spi.SqlArrayMultiKeyLoader;
+import org.hibernate.metamodel.mapping.JdbcMapping;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
+import org.hibernate.metamodel.mapping.internal.SimpleForeignKeyDescriptor;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterImpl;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
+import org.hibernate.sql.results.spi.ListResultsConsumer;
+import org.hibernate.type.BasicType;
+
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_DEBUG_ENABLED;
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER;
+
+/**
+ * CollectionBatchLoader using a SQL ARRAY parameter to pass the key values
+ *
+ * @author Steve Ebersole
+ */
+public class CollectionBatchLoaderArrayParam
+		extends AbstractCollectionBatchLoader
+		implements CollectionBatchLoader, SqlArrayMultiKeyLoader {
+	private final  Class<?> arrayElementType;
+	private final JdbcMapping arrayJdbcMapping;
+	private final JdbcParameter jdbcParameter;
+	private final SelectStatement sqlSelect;
+	private final JdbcOperationQuerySelect jdbcSelectOperation;
+
+	public CollectionBatchLoaderArrayParam(
+			int domainBatchSize,
+			LoadQueryInfluencers loadQueryInfluencers,
+			PluralAttributeMapping attributeMapping,
+			SessionFactoryImplementor sessionFactory) {
+		super( domainBatchSize, loadQueryInfluencers, attributeMapping, sessionFactory );
+
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf(
+					"Using ARRAY batch fetching strategy for collection `%s` : %s",
+					attributeMapping.getNavigableRole().getFullPath(),
+					domainBatchSize
+			);
+		}
+
+		final SimpleForeignKeyDescriptor keyDescriptor = (SimpleForeignKeyDescriptor) getLoadable().getKeyDescriptor();
+
+		arrayElementType = keyDescriptor.getJavaType().getJavaTypeClass();
+		Class<?> arrayClass = Array.newInstance( arrayElementType, 0 ).getClass();
+
+		final BasicType<?> arrayBasicType = getSessionFactory().getTypeConfiguration()
+				.getBasicTypeRegistry()
+				.getRegisteredType( arrayClass );
+		arrayJdbcMapping = MultiKeyLoadHelper.resolveArrayJdbcMapping(
+				arrayBasicType,
+				keyDescriptor.getJdbcMapping(),
+				arrayClass,
+				getSessionFactory()
+		);
+
+		jdbcParameter = new JdbcParameterImpl( arrayJdbcMapping );
+		sqlSelect = LoaderSelectBuilder.createSelectBySingleArrayParameter(
+				getLoadable(),
+				keyDescriptor.getKeyPart(),
+				getInfluencers(),
+				LockOptions.NONE,
+				jdbcParameter,
+				getSessionFactory()
+		);
+
+		jdbcSelectOperation = getSessionFactory().getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( getSessionFactory(), sqlSelect )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+	}
+
+	@Override
+	public PersistentCollection<?> load(Object key, SharedSessionContractImplementor session) {
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf( "Batch loading entity `%s#%s`", getLoadable().getNavigableRole().getFullPath(), key );
+		}
+
+		final Object[] keysToInitialize = resolveKeysToInitialize( key, session );
+		initializeKeys( keysToInitialize, session );
+
+		for ( int i = 0; i < keysToInitialize.length; i++ ) {
+			finishInitializingKey( keysToInitialize[i], session );
+		}
+
+		final CollectionKey collectionKey = new CollectionKey( getLoadable().getCollectionDescriptor(), key );
+		return session.getPersistenceContext().getCollection( collectionKey );
+	}
+
+	private Object[] resolveKeysToInitialize(Object keyBeingLoaded, SharedSessionContractImplementor session) {
+		final Object[] keysToInitialize = (Object[]) Array.newInstance( arrayElementType, getDomainBatchSize() );
+		session.getPersistenceContextInternal().getBatchFetchQueue().collectBatchLoadableCollectionKeys(
+				getDomainBatchSize(),
+				(index, value) -> keysToInitialize[index] = value,
+				keyBeingLoaded,
+				getLoadable()
+		);
+		return keysToInitialize;
+	}
+
+	private void initializeKeys(Object[] keysToInitialize, SharedSessionContractImplementor session) {
+		assert jdbcSelectOperation != null;
+		assert jdbcParameter != null;
+
+		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl(1);
+		jdbcParameterBindings.addBinding(
+				jdbcParameter,
+				new JdbcParameterBindingImpl( arrayJdbcMapping, keysToInitialize )
+		);
+
+		final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
+				session.getPersistenceContext().getBatchFetchQueue(),
+				sqlSelect,
+				Collections.singletonList( jdbcParameter ),
+				jdbcParameterBindings
+		);
+
+		session.getJdbcServices().getJdbcSelectExecutor().list(
+				jdbcSelectOperation,
+				jdbcParameterBindings,
+				new SingleIdExecutionContext(
+						null,
+						null,
+						null,
+						LockOptions.NONE,
+						subSelectFetchableKeysHandler,
+						session
+				),
+				RowTransformerStandardImpl.instance(),
+				ListResultsConsumer.UniqueSemantic.FILTER
+		);
+	}
+
+	public void prepare() {
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/CollectionBatchLoaderInPredicate.java

@@ -0,0 +1,209 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.hibernate.LockOptions;
+import org.hibernate.collection.spi.PersistentCollection;
+import org.hibernate.engine.spi.BatchFetchQueue;
+import org.hibernate.engine.spi.CollectionKey;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.engine.spi.SubselectFetch;
+import org.hibernate.internal.util.MutableInteger;
+import org.hibernate.internal.util.collections.CollectionHelper;
+import org.hibernate.loader.ast.spi.CollectionBatchLoader;
+import org.hibernate.loader.ast.spi.SqlArrayMultiKeyLoader;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_DEBUG_ENABLED;
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER;
+
+/**
+ * CollectionLoader for batch fetching using a SQL IN predicate
+ *
+ * @author Steve Ebersole
+ */
+public class CollectionBatchLoaderInPredicate
+		extends AbstractCollectionBatchLoader
+		implements CollectionBatchLoader, SqlArrayMultiKeyLoader {
+	private final int keyColumnCount;
+	private final int sqlBatchSize;
+	private final List<JdbcParameter> jdbcParameters;
+	private final SelectStatement sqlAst;
+	private final JdbcOperationQuerySelect jdbcSelect;
+
+	private CollectionLoaderSingleKey singleKeyLoader;
+
+	public CollectionBatchLoaderInPredicate(
+			int domainBatchSize,
+			LoadQueryInfluencers influencers,
+			PluralAttributeMapping attributeMapping,
+			SessionFactoryImplementor sessionFactory) {
+		super( domainBatchSize, influencers, attributeMapping, sessionFactory );
+
+		this.keyColumnCount = attributeMapping.getKeyDescriptor().getJdbcTypeCount();
+		this.sqlBatchSize = sessionFactory.getJdbcServices()
+				.getDialect()
+				.getBatchLoadSizingStrategy()
+				.determineOptimalBatchLoadSize( keyColumnCount, domainBatchSize, false );
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf(
+					"Using IN-predicate batch fetching strategy for collection `%s` : %s (%s)",
+					attributeMapping.getNavigableRole().getFullPath(),
+					sqlBatchSize,
+					domainBatchSize
+			);
+		}
+
+		this.jdbcParameters = new ArrayList<>();
+		this.sqlAst = LoaderSelectBuilder.createSelect(
+				attributeMapping,
+				null,
+				attributeMapping.getKeyDescriptor(),
+				null,
+				sqlBatchSize,
+				influencers,
+				LockOptions.NONE,
+				jdbcParameters::add,
+				sessionFactory
+		);
+		assert this.jdbcParameters.size() == this.sqlBatchSize * this.keyColumnCount;
+
+		this.jdbcSelect = sessionFactory.getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( sessionFactory, sqlAst )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+	}
+
+	@Override
+	public PersistentCollection<?> load(
+			Object key,
+			SharedSessionContractImplementor session) {
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf( "Loading collection `%s#%s` by batch-fetch", getLoadable().getNavigableRole().getFullPath(), key );
+		}
+
+		final MutableInteger nonNullCounter = new MutableInteger();
+		final ArrayList<Object> keysToInitialize = CollectionHelper.arrayList( getDomainBatchSize() );
+		session.getPersistenceContextInternal().getBatchFetchQueue().collectBatchLoadableCollectionKeys(
+				getDomainBatchSize(),
+				(index, batchableKey) -> {
+					keysToInitialize.add( batchableKey );
+					if ( batchableKey != null ) {
+						nonNullCounter.increment();
+					}
+				},
+				key,
+				getLoadable().asPluralAttributeMapping()
+		);
+
+		if ( nonNullCounter.get() <= 0 ) {
+			throw new IllegalStateException( "Number of non-null collection keys to batch fetch should never be 0" );
+		}
+
+		if ( nonNullCounter.get() == 1 ) {
+			prepareSingleKeyLoaderIfNeeded();
+			return singleKeyLoader.load( key, session );
+		}
+
+		initializeKeys( key, keysToInitialize.toArray( keysToInitialize.toArray( new Object[0] ) ), nonNullCounter.get(), session );
+
+		final CollectionKey collectionKey = new CollectionKey( getLoadable().getCollectionDescriptor(), key );
+		return session.getPersistenceContext().getCollection( collectionKey );
+	}
+
+	private void prepareSingleKeyLoaderIfNeeded() {
+		if ( singleKeyLoader == null ) {
+			singleKeyLoader = new CollectionLoaderSingleKey( getLoadable(), getInfluencers(), getSessionFactory() );
+		}
+	}
+
+	private <T> void initializeKeys(
+			T key,
+			T[] keysToInitialize,
+			int nonNullKeysToInitializeCount,
+			SharedSessionContractImplementor session) {
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf(
+					"Collection keys to batch-fetch initialize (`%s#%s`) %s",
+					getLoadable().getNavigableRole().getFullPath(),
+					key,
+					keysToInitialize
+			);
+		}
+
+		final MultiKeyLoadChunker<T> chunker = new MultiKeyLoadChunker<>(
+				sqlBatchSize,
+				keyColumnCount,
+				getLoadable().getKeyDescriptor(),
+				jdbcParameters,
+				sqlAst,
+				jdbcSelect
+		);
+
+		final BatchFetchQueue batchFetchQueue = session.getPersistenceContextInternal().getBatchFetchQueue();
+
+		chunker.processChunks(
+				keysToInitialize,
+				nonNullKeysToInitializeCount,
+				(jdbcParameterBindings, session1) -> {
+					// Create a RegistrationHandler for handling any subselect fetches we encounter handling this chunk
+					final SubselectFetch.RegistrationHandler registrationHandler = SubselectFetch.createRegistrationHandler(
+							batchFetchQueue,
+							sqlAst,
+							jdbcParameters,
+							jdbcParameterBindings
+					);
+					return new ExecutionContextWithSubselectFetchHandler( session, registrationHandler );
+				},
+				(key1, relativePosition, absolutePosition) -> {
+				},
+				(startIndex) -> {
+					if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+						MULTI_KEY_LOAD_LOGGER.debugf(
+								"Processing collection batch-fetch chunk (`%s#%s`) %s - %s",
+								getLoadable().getNavigableRole().getFullPath(),
+								key,
+								startIndex,
+								startIndex + (sqlBatchSize-1)
+						);
+					}
+				},
+				(startIndex, nonNullElementCount) -> {
+					if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+						MULTI_KEY_LOAD_LOGGER.debugf(
+								"Finishing collection batch-fetch chunk (`%s#%s`) %s - %s (%s)",
+								getLoadable().getNavigableRole().getFullPath(),
+								key,
+								startIndex,
+								startIndex + (sqlBatchSize-1),
+								nonNullElementCount
+						);
+					}
+					for ( int i = 0; i < nonNullElementCount; i++ ) {
+						final int keyPosition = i + startIndex;
+						if ( keyPosition < keysToInitialize.length ) {
+							final T keyToInitialize = keysToInitialize[keyPosition];
+							finishInitializingKey( keyToInitialize, session );
+						}
+					}
+				},
+				session
+		);
+	}
+
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/CollectionLoaderBatchKey.java

@@ -1,235 +0,0 @@
-/*
- * Hibernate, Relational Persistence for Idiomatic Java
- *
- * License: GNU Lesser General Public License (LGPL), version 2.1 or later
- * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
- */
-package org.hibernate.loader.ast.internal;
-
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-
-import org.hibernate.LockOptions;
-import org.hibernate.collection.spi.PersistentCollection;
-import org.hibernate.engine.jdbc.env.spi.JdbcEnvironment;
-import org.hibernate.engine.jdbc.spi.JdbcServices;
-import org.hibernate.engine.spi.CollectionEntry;
-import org.hibernate.engine.spi.CollectionKey;
-import org.hibernate.engine.spi.LoadQueryInfluencers;
-import org.hibernate.engine.spi.PersistenceContext;
-import org.hibernate.engine.spi.SessionFactoryImplementor;
-import org.hibernate.engine.spi.SharedSessionContractImplementor;
-import org.hibernate.engine.spi.SubselectFetch;
-import org.hibernate.internal.util.collections.ArrayHelper;
-import org.hibernate.loader.ast.spi.CollectionLoader;
-import org.hibernate.metamodel.mapping.PluralAttributeMapping;
-import org.hibernate.query.spi.QueryOptions;
-import org.hibernate.sql.ast.SqlAstTranslatorFactory;
-import org.hibernate.sql.ast.tree.expression.JdbcParameter;
-import org.hibernate.sql.ast.tree.select.SelectStatement;
-import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
-import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
-import org.hibernate.sql.exec.spi.JdbcParameterBindings;
-import org.hibernate.sql.results.internal.ResultsHelper;
-import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
-import org.hibernate.sql.results.spi.ListResultsConsumer;
-
-import org.jboss.logging.Logger;
-
-/**
- * A one-time use CollectionLoader for applying a batch fetch
- *
- * @author Steve Ebersole
- */
-public class CollectionLoaderBatchKey implements CollectionLoader {
-	private static final Logger log = Logger.getLogger( CollectionLoaderBatchKey.class );
-
-	private final PluralAttributeMapping attributeMapping;
-	private final int batchSize;
-
-	private final int keyJdbcCount;
-
-	private SelectStatement batchSizeSqlAst;
-	private List<JdbcParameter> batchSizeJdbcParameters;
-
-	public CollectionLoaderBatchKey(
-			PluralAttributeMapping attributeMapping,
-			int batchSize,
-			LoadQueryInfluencers influencers,
-			SessionFactoryImplementor sessionFactory) {
-		this.attributeMapping = attributeMapping;
-		this.batchSize = batchSize;
-
-		this.keyJdbcCount = attributeMapping.getKeyDescriptor().getJdbcTypeCount();
-
-		this.batchSizeJdbcParameters = new ArrayList<>();
-		this.batchSizeSqlAst = LoaderSelectBuilder.createSelect(
-				attributeMapping,
-				null,
-				attributeMapping.getKeyDescriptor(),
-				null,
-				batchSize,
-				influencers,
-				LockOptions.NONE,
-				batchSizeJdbcParameters::add,
-				sessionFactory
-		);
-	}
-
-	@Override
-	public PluralAttributeMapping getLoadable() {
-		return attributeMapping;
-	}
-
-	@Override
-	public PersistentCollection<?> load(
-			Object key,
-			SharedSessionContractImplementor session) {
-		final Object[] batchIds = session.getPersistenceContextInternal()
-				.getBatchFetchQueue()
-				.getCollectionBatch( getLoadable().getCollectionDescriptor(), key, batchSize );
-
-		final int numberOfIds = ArrayHelper.countNonNull( batchIds );
-
-		if ( numberOfIds == 1 ) {
-			final List<JdbcParameter> jdbcParameters = new ArrayList<>( keyJdbcCount );
-			final SelectStatement sqlAst = LoaderSelectBuilder.createSelect(
-					attributeMapping,
-					null,
-					attributeMapping.getKeyDescriptor(),
-					null,
-					1,
-					session.getLoadQueryInfluencers(),
-					LockOptions.NONE,
-					jdbcParameters::add,
-					session.getFactory()
-			);
-
-			new SingleIdLoadPlan(
-					null,
-					attributeMapping.getKeyDescriptor(),
-					sqlAst,
-					jdbcParameters,
-					LockOptions.NONE,
-					session.getFactory()
-			).load( key, session );
-		}
-		else {
-			batchLoad( batchIds, numberOfIds , session );
-		}
-
-		final CollectionKey collectionKey = new CollectionKey( attributeMapping.getCollectionDescriptor(), key );
-		return session.getPersistenceContext().getCollection( collectionKey );
-	}
-
-	private void batchLoad(
-			Object[] batchIds,
-			int numberOfIds,
-			SharedSessionContractImplementor session) {
-		if ( log.isDebugEnabled() ) {
-			log.debugf(
-					"Batch loading collection [%s] : %s",
-					getLoadable().getCollectionDescriptor().getRole(),
-					batchIds
-			);
-		}
-
-		int smallBatchStart = 0;
-		int smallBatchLength = Math.min( numberOfIds, batchSize );
-
-		while ( true ) {
-			final List<JdbcParameter> jdbcParameters;
-			final SelectStatement sqlAst;
-
-			if ( smallBatchLength == batchSize ) {
-				jdbcParameters = this.batchSizeJdbcParameters;
-				sqlAst = this.batchSizeSqlAst;
-			}
-			else {
-				jdbcParameters = new ArrayList<>();
-				sqlAst = LoaderSelectBuilder.createSelect(
-						getLoadable(),
-						// null here means to select everything
-						null,
-						getLoadable().getKeyDescriptor(),
-						null,
-						numberOfIds,
-						session.getLoadQueryInfluencers(),
-						LockOptions.NONE,
-						jdbcParameters::add,
-						session.getFactory()
-				);
-			}
-
-			final SessionFactoryImplementor sessionFactory = session.getFactory();
-			final JdbcServices jdbcServices = sessionFactory.getJdbcServices();
-			final JdbcEnvironment jdbcEnvironment = jdbcServices.getJdbcEnvironment();
-			final SqlAstTranslatorFactory sqlAstTranslatorFactory = jdbcEnvironment.getSqlAstTranslatorFactory();
-
-			final JdbcOperationQuerySelect jdbcSelect = sqlAstTranslatorFactory
-					.buildSelectTranslator( sessionFactory, sqlAst )
-					.translate( null, QueryOptions.NONE );
-
-			final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl( keyJdbcCount * smallBatchLength );
-
-			int offset = 0;
-
-			for ( int i = smallBatchStart; i < smallBatchStart + smallBatchLength; i++ ) {
-				offset += jdbcParameterBindings.registerParametersForEachJdbcValue(
-						batchIds[i],
-						offset,
-						getLoadable().getKeyDescriptor(),
-						jdbcParameters,
-						session
-				);
-			}
-			assert offset == jdbcParameters.size();
-
-			final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
-					session.getPersistenceContext().getBatchFetchQueue(),
-					sqlAst,
-					Collections.emptyList(),
-					jdbcParameterBindings
-			);
-
-			jdbcServices.getJdbcSelectExecutor().list(
-					jdbcSelect,
-					jdbcParameterBindings,
-					new ExecutionContextWithSubselectFetchHandler( session, subSelectFetchableKeysHandler ),
-					RowTransformerStandardImpl.instance(),
-					ListResultsConsumer.UniqueSemantic.FILTER
-			);
-
-			for ( int i = smallBatchStart; i < smallBatchStart + smallBatchLength; i++ ) {
-				// collections that were not initialized here should be empty
-				finishLoadingCollection( batchIds[i], session );
-			}
-
-			// prepare for the next round...
-			smallBatchStart += smallBatchLength;
-			if ( smallBatchStart >= numberOfIds ) {
-				break;
-			}
-
-			smallBatchLength = Math.min( numberOfIds - smallBatchStart, batchSize );
-		}
-	}
-
-	private void finishLoadingCollection(Object key, SharedSessionContractImplementor session) {
-		final PersistenceContext persistenceContext = session.getPersistenceContext();
-		final CollectionKey collectionKey = new CollectionKey( attributeMapping.getCollectionDescriptor(), key );
-		final PersistentCollection<?> collection = persistenceContext.getCollection( collectionKey );
-		if ( !collection.wasInitialized() ) {
-			final CollectionEntry entry = persistenceContext.getCollectionEntry( collection );
-			collection.initializeEmptyCollection( entry.getLoadedPersister() );
-			ResultsHelper.finalizeCollectionLoading(
-					persistenceContext,
-					entry.getLoadedPersister(),
-					collection,
-					collectionKey,
-					true
-			);
-		}
-	}
-}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/EntityBatchLoaderArrayParam.java

@@ -0,0 +1,202 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.lang.reflect.Array;
+import java.util.Collections;
+import java.util.Locale;
+
+import org.hibernate.LockOptions;
+import org.hibernate.engine.internal.BatchFetchQueueHelper;
+import org.hibernate.engine.spi.EntityKey;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.engine.spi.SubselectFetch;
+import org.hibernate.loader.ast.spi.EntityBatchLoader;
+import org.hibernate.loader.ast.spi.SqlArrayMultiKeyLoader;
+import org.hibernate.metamodel.mapping.BasicEntityIdentifierMapping;
+import org.hibernate.metamodel.mapping.EntityIdentifierMapping;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.metamodel.mapping.JdbcMapping;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterImpl;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
+import org.hibernate.sql.results.spi.ListResultsConsumer;
+import org.hibernate.type.BasicType;
+import org.hibernate.type.BasicTypeRegistry;
+
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_DEBUG_ENABLED;
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER;
+
+/**
+ * SingleIdEntityLoaderSupport implementation based on using a single
+ * {@linkplain org.hibernate.type.SqlTypes#ARRAY array} parameter to pass the
+ * entire batch of ids.
+ *
+ * @author Steve Ebersole
+ */
+public class EntityBatchLoaderArrayParam<T>
+		extends SingleIdEntityLoaderSupport<T>
+		implements EntityBatchLoader<T>, SqlArrayMultiKeyLoader, Preparable {
+	private final int domainBatchSize;
+
+	private BasicEntityIdentifierMapping identifierMapping;
+	private JdbcMapping arrayJdbcMapping;
+	private JdbcParameter jdbcParameter;
+	private SelectStatement sqlAst;
+	private JdbcOperationQuerySelect jdbcSelectOperation;
+
+
+	/**
+	 * Instantiates the loader
+	 *
+	 * @param domainBatchSize The number of domain model parts (up to)
+	 *
+	 * @implNote We delay initializing the internal SQL AST state until first use.  Creating
+	 * the SQL AST internally relies on the entity's {@link EntityIdentifierMapping}. However, we
+	 * do create the static batch-loader for the entity in the persister constructor and
+	 * {@link EntityIdentifierMapping} is not available at that time.  On first use, we know we
+	 * have it available
+	 */
+	public EntityBatchLoaderArrayParam(
+			int domainBatchSize,
+			EntityMappingType entityDescriptor,
+			SessionFactoryImplementor sessionFactory) {
+		super( entityDescriptor, sessionFactory );
+		this.domainBatchSize = domainBatchSize;
+
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf(
+					"Batch fetching enabled for `%s` (entity) using ARRAY strategy : %s",
+					entityDescriptor.getEntityName(),
+					domainBatchSize
+			);
+		}
+	}
+
+	@Override
+	public int getDomainBatchSize() {
+		return domainBatchSize;
+	}
+
+	@Override
+	public final T load(
+			Object pkValue,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf( "Batch fetching entity `%s#%s`", getLoadable().getEntityName(), pkValue );
+		}
+
+		final Object[] ids = resolveIdsToInitialize( pkValue, session );
+		initializeEntities( ids, pkValue, entityInstance, lockOptions, readOnly, session );
+
+		final EntityKey entityKey = session.generateEntityKey( pkValue, getLoadable().getEntityPersister() );
+		//noinspection unchecked
+		return (T) session.getPersistenceContext().getEntity( entityKey );
+	}
+
+	protected Object[] resolveIdsToInitialize(Object pkValue, SharedSessionContractImplementor session) {
+		final Object[] idsToLoad = (Object[]) Array.newInstance( identifierMapping.getJavaType().getJavaTypeClass(), domainBatchSize );
+		session.getPersistenceContextInternal().getBatchFetchQueue().collectBatchLoadableEntityIds(
+				domainBatchSize,
+				(index, value) -> idsToLoad[index] = value,
+				pkValue,
+				getLoadable()
+		);
+		return idsToLoad;
+	}
+
+	private void initializeEntities(
+			Object[] idsToInitialize,
+			Object pkValue,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		LoaderHelper.loadByArrayParameter(
+				idsToInitialize,
+				sqlAst,
+				jdbcSelectOperation,
+				jdbcParameter,
+				arrayJdbcMapping,
+				pkValue,
+				entityInstance,
+				lockOptions,
+				readOnly,
+				session
+		);
+
+		//noinspection ForLoopReplaceableByForEach
+		for ( int i = 0; i < idsToInitialize.length; i++ ) {
+			final Object id = idsToInitialize[i];
+			if ( id == null ) {
+				// skip any of the null padded ids
+				//		- actually we could probably even break here
+				continue;
+			}
+			// found or not, remove the key from the batch-fetch queue
+			BatchFetchQueueHelper.removeBatchLoadableEntityKey( id, getLoadable(), session );
+		}
+	}
+
+	@Override
+	public T load(Object pkValue, LockOptions lockOptions, Boolean readOnly, SharedSessionContractImplementor session) {
+		return load( pkValue, null, lockOptions, readOnly, session );
+	}
+
+	@Override
+	public void prepare() {
+		identifierMapping = (BasicEntityIdentifierMapping) getLoadable().getIdentifierMapping();
+		final Class<?> arrayClass = Array.newInstance( identifierMapping.getJavaType().getJavaTypeClass(), 0 ).getClass();
+
+		final BasicTypeRegistry basicTypeRegistry = sessionFactory.getTypeConfiguration().getBasicTypeRegistry();
+		final BasicType<?> arrayBasicType = basicTypeRegistry.getRegisteredType( arrayClass );
+
+		arrayJdbcMapping = MultiKeyLoadHelper.resolveArrayJdbcMapping(
+				arrayBasicType,
+				identifierMapping.getJdbcMapping(),
+				arrayClass,
+				sessionFactory
+		);
+
+		jdbcParameter = new JdbcParameterImpl( arrayJdbcMapping );
+		sqlAst = LoaderSelectBuilder.createSelectBySingleArrayParameter(
+				getLoadable(),
+				identifierMapping,
+				LoadQueryInfluencers.NONE,
+				LockOptions.NONE,
+				jdbcParameter,
+				sessionFactory
+		);
+
+		jdbcSelectOperation = sessionFactory.getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( sessionFactory, sqlAst )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+	}
+
+	@Override
+	public String toString() {
+		return String.format(
+				Locale.ROOT,
+				"EntityBatchLoaderArrayParam(%s [%s])",
+				getLoadable().getEntityName(),
+				domainBatchSize
+		);
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/EntityBatchLoaderInPredicate.java

@@ -0,0 +1,337 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+
+import org.hibernate.LockOptions;
+import org.hibernate.engine.spi.BatchFetchQueue;
+import org.hibernate.engine.spi.EntityKey;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.engine.spi.SubselectFetch;
+import org.hibernate.loader.ast.spi.EntityBatchLoader;
+import org.hibernate.loader.ast.spi.SqlInPredicateMultiKeyLoader;
+import org.hibernate.metamodel.mapping.EntityIdentifierMapping;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
+import org.hibernate.sql.results.spi.ListResultsConsumer;
+
+import static org.hibernate.internal.util.collections.CollectionHelper.arrayList;
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_DEBUG_ENABLED;
+import static org.hibernate.loader.ast.internal.MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER;
+
+/**
+ * An EntityBatchLoader using one or more SQL queries, which each initialize up to
+ * {@linkplain #getSqlBatchSize()} entities using a SQL IN predicate restriction -
+ * e.g., {@code ... where id in (?,?,...)}.
+ * <p/>
+ * The number of parameters rendered into the SQL is controlled by {@linkplain #getSqlBatchSize()}.
+ * Any unused parameter slots for a particular execution are set to {@code null}.
+ *
+ * @author Steve Ebersole
+ */
+public class EntityBatchLoaderInPredicate<T>
+		extends SingleIdEntityLoaderSupport<T>
+		implements EntityBatchLoader<T>, SqlInPredicateMultiKeyLoader, Preparable {
+	private final int domainBatchSize;
+	private final int sqlBatchSize;
+
+	private List<JdbcParameter> jdbcParameters;
+	private SelectStatement sqlAst;
+	private JdbcOperationQuerySelect jdbcSelectOperation;
+
+	/**
+	 * @param domainBatchSize The maximum number of entities we will initialize for each {@link #load load}
+	 * @param sqlBatchSize The number of keys our SQL AST should be able to fetch
+	 */
+	public EntityBatchLoaderInPredicate(
+			int domainBatchSize,
+			int sqlBatchSize,
+			EntityMappingType entityDescriptor,
+			SessionFactoryImplementor sessionFactory) {
+		super( entityDescriptor, sessionFactory );
+		this.domainBatchSize = domainBatchSize;
+		this.sqlBatchSize = sqlBatchSize;
+
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf(
+					"Batch fetching `%s` entity using padded IN-list : %s (%s)",
+					entityDescriptor.getEntityName(),
+					domainBatchSize,
+					sqlBatchSize
+			);
+		}
+	}
+
+	@Override
+	public int getDomainBatchSize() {
+		return domainBatchSize;
+	}
+
+	public int getSqlBatchSize() {
+		return sqlBatchSize;
+	}
+
+	@Override
+	public final T load(Object pkValue, LockOptions lockOptions, Boolean readOnly, SharedSessionContractImplementor session) {
+		return load( pkValue, null, lockOptions, readOnly, session );
+	}
+
+	@Override
+	public final T load(
+			Object pkValue,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf( "Batch loading entity `%s#%s`", getLoadable().getEntityName(), pkValue );
+		}
+
+		final Object[] idsToInitialize = resolveIdsToLoad( pkValue, session );
+		if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+			MULTI_KEY_LOAD_LOGGER.debugf( "Ids to batch-fetch initialize (`%s#%s`) %s", getLoadable().getEntityName(), pkValue, Arrays.toString(idsToInitialize) );
+		}
+
+		initializeEntities( idsToInitialize, pkValue, entityInstance, lockOptions, readOnly, session );
+
+		final EntityKey entityKey = session.generateEntityKey( pkValue, getLoadable().getEntityPersister() );
+		//noinspection unchecked
+		return (T) session.getPersistenceContext().getEntity( entityKey );
+	}
+
+	protected Object[] resolveIdsToLoad(Object pkValue, SharedSessionContractImplementor session) {
+		return session.getPersistenceContextInternal().getBatchFetchQueue().getBatchLoadableEntityIds(
+				getLoadable(),
+				pkValue,
+				domainBatchSize
+		);
+	}
+
+	protected void initializeEntities(
+			Object[] idsToInitialize,
+			Object pkValue,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		final MultiKeyLoadChunker<Object> chunker = new MultiKeyLoadChunker<>(
+				sqlBatchSize,
+				getLoadable().getIdentifierMapping().getJdbcTypeCount(),
+				getLoadable().getIdentifierMapping(),
+				jdbcParameters,
+				sqlAst,
+				jdbcSelectOperation
+		);
+
+		final BatchFetchQueue batchFetchQueue = session.getPersistenceContextInternal().getBatchFetchQueue();
+		final List<EntityKey> entityKeys = arrayList( sqlBatchSize );
+
+		chunker.processChunks(
+				idsToInitialize,
+				sqlBatchSize,
+				(jdbcParameterBindings, session1) -> {
+					// Create a RegistrationHandler for handling any subselect fetches we encounter handling this chunk
+					final SubselectFetch.RegistrationHandler registrationHandler = SubselectFetch.createRegistrationHandler(
+							batchFetchQueue,
+							sqlAst,
+							jdbcParameters,
+							jdbcParameterBindings
+					);
+					return new SingleIdExecutionContext(
+							pkValue,
+							entityInstance,
+							readOnly,
+							lockOptions,
+							registrationHandler,
+							session
+					);
+				},
+				(key, relativePosition, absolutePosition) -> {
+					if ( key != null ) {
+						entityKeys.add( session.generateEntityKey( key, getLoadable().getEntityPersister() ) );
+					}
+				},
+				(startIndex) -> {
+					if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+						MULTI_KEY_LOAD_LOGGER.debugf(
+								"Processing entity batch-fetch chunk (`%s#%s`) %s - %s",
+								getLoadable().getEntityName(),
+								pkValue,
+								startIndex,
+								startIndex + ( sqlBatchSize -1)
+						);
+					}
+				},
+				(startIndex, nonNullElementCount) -> {
+					entityKeys.forEach( batchFetchQueue::removeBatchLoadableEntityKey );
+					entityKeys.clear();
+				},
+				session
+		);
+
+
+
+//		int numberOfIdsLeft = idsToInitialize.length;
+//		int start = 0;
+//		while ( numberOfIdsLeft > 0 ) {
+//			if ( MULTI_KEY_LOAD_DEBUG_ENABLED ) {
+//				MULTI_KEY_LOAD_LOGGER.debugf( "Processing batch-fetch chunk (`%s#%s`) %s - %s", getLoadable().getEntityName(), pkValue, start, start + ( sqlBatchSize -1) );
+//			}
+//			initializeChunk( idsToInitialize, start, pkValue, entityInstance, lockOptions, readOnly, session );
+//
+//			start += sqlBatchSize;
+//			numberOfIdsLeft -= sqlBatchSize;
+//		}
+	}
+
+	private void initializeChunk(
+			Object[] idsToInitialize,
+			int start,
+			Object pkValue,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		initializeChunk(
+				idsToInitialize,
+				getLoadable(),
+				start,
+				sqlBatchSize,
+				jdbcParameters,
+				sqlAst,
+				jdbcSelectOperation,
+				pkValue,
+				entityInstance,
+				lockOptions,
+				readOnly,
+				session
+		);
+	}
+
+	private static void initializeChunk(
+			Object[] idsToInitialize,
+			EntityMappingType entityMapping,
+			int startIndex,
+			int numberOfKeys,
+			List<JdbcParameter> jdbcParameters,
+			SelectStatement sqlAst,
+			JdbcOperationQuerySelect jdbcSelectOperation,
+			Object pkValue,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		final BatchFetchQueue batchFetchQueue = session.getPersistenceContext().getBatchFetchQueue();
+
+		final int numberOfJdbcParameters = entityMapping.getIdentifierMapping().getJdbcTypeCount() * numberOfKeys;
+		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl( numberOfJdbcParameters );
+
+		final List<EntityKey> entityKeys = arrayList( numberOfKeys );
+		int bindCount = 0;
+		for ( int i = 0; i < numberOfKeys; i++ ) {
+			final int idPosition = i + startIndex;
+			final Object value;
+			if ( idPosition >= idsToInitialize.length ) {
+				value = null;
+			}
+			else {
+				value = idsToInitialize[idPosition];
+			}
+			if ( value != null ) {
+				entityKeys.add( session.generateEntityKey( value, entityMapping.getEntityPersister() ) );
+			}
+			bindCount += jdbcParameterBindings.registerParametersForEachJdbcValue(
+					value,
+					bindCount,
+					entityMapping.getIdentifierMapping(),
+					jdbcParameters,
+					session
+			);
+		}
+		assert bindCount == jdbcParameters.size();
+
+		if ( entityKeys.isEmpty() ) {
+			// there are no non-null keys in the chunk
+			return;
+		}
+
+		// Create a SubselectFetch.RegistrationHandler for handling any subselect fetches we encounter here
+		final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
+				batchFetchQueue,
+				sqlAst,
+				jdbcParameters,
+				jdbcParameterBindings
+		);
+
+		session.getJdbcServices().getJdbcSelectExecutor().list(
+				jdbcSelectOperation,
+				jdbcParameterBindings,
+				new SingleIdExecutionContext(
+						pkValue,
+						entityInstance,
+						readOnly,
+						lockOptions,
+						subSelectFetchableKeysHandler,
+						session
+				),
+				RowTransformerStandardImpl.instance(),
+				ListResultsConsumer.UniqueSemantic.FILTER
+		);
+
+		entityKeys.forEach( batchFetchQueue::removeBatchLoadableEntityKey );
+	}
+
+	@Override
+	public void prepare() {
+		EntityIdentifierMapping identifierMapping = getLoadable().getIdentifierMapping();
+
+		final int expectedNumberOfParameters = identifierMapping.getJdbcTypeCount() * sqlBatchSize;
+
+		jdbcParameters = arrayList( expectedNumberOfParameters );
+		sqlAst = LoaderSelectBuilder.createSelect(
+				getLoadable(),
+				// null here means to select everything
+				null,
+				identifierMapping,
+				null,
+				sqlBatchSize,
+				LoadQueryInfluencers.NONE,
+				LockOptions.NONE,
+				jdbcParameters::add,
+				sessionFactory
+		);
+		assert jdbcParameters.size() == expectedNumberOfParameters;
+
+		jdbcSelectOperation = sessionFactory.getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( sessionFactory, sqlAst )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+	}
+
+	@Override
+	public String toString() {
+		return String.format(
+				Locale.ROOT,
+				"EntityBatchLoaderInPredicate(%s [%s (%s)])",
+				getLoadable().getEntityName(),
+				domainBatchSize,
+				sqlBatchSize
+		);
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/LoaderHelper.java

@@ -6,23 +6,46 @@
  */
 package org.hibernate.loader.ast.internal;
 
+import java.lang.reflect.Array;
+import java.util.Collections;
+import java.util.List;
+
 import org.hibernate.LockMode;
 import org.hibernate.LockOptions;
 import org.hibernate.ObjectDeletedException;
 import org.hibernate.cache.spi.access.EntityDataAccess;
 import org.hibernate.cache.spi.access.SoftLock;
 import org.hibernate.engine.spi.EntityEntry;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.engine.spi.Status;
+import org.hibernate.engine.spi.SubselectFetch;
 import org.hibernate.event.spi.EventSource;
 import org.hibernate.loader.LoaderLogging;
+import org.hibernate.metamodel.mapping.BasicValuedModelPart;
+import org.hibernate.metamodel.mapping.JdbcMapping;
 import org.hibernate.persister.entity.EntityPersister;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
+import org.hibernate.sql.results.spi.ListResultsConsumer;
+import org.hibernate.type.descriptor.java.JavaType;
 
 /**
  * @author Steve Ebersole
  */
 public class LoaderHelper {
 
+	/**
+	 * Ensure the {@linkplain LockMode} associated with the entity in relation to a
+	 * persistence context is {@linkplain LockMode#greaterThan great or equal} to the
+	 * requested mode.
+	 */
 	public static void upgradeLock(Object object, EntityEntry entry, LockOptions lockOptions, EventSource session) {
 		LockMode requestedLockMode = lockOptions.getLockMode();
 		if ( requestedLockMode.greaterThan( entry.getLockMode() ) ) {
@@ -80,4 +103,125 @@ public class LoaderHelper {
 
 		}
 	}
+
+	/**
+	 * Determine if the influencers associated with the given Session indicate read-only
+	 */
+	public static Boolean getReadOnlyFromLoadQueryInfluencers(SharedSessionContractImplementor session) {
+		return getReadOnlyFromLoadQueryInfluencers( session.getLoadQueryInfluencers() );
+	}
+
+	/**
+	 * Determine if given influencers indicate read-only
+	 */
+	public static Boolean getReadOnlyFromLoadQueryInfluencers(LoadQueryInfluencers loadQueryInfluencers) {
+		if ( loadQueryInfluencers == null ) {
+			return null;
+		}
+		return loadQueryInfluencers.getReadOnly();
+	}
+
+	/**
+	 * Normalize an array of keys (primary, foreign or natural).
+	 * <p/>
+	 * If the array is already typed as the key type, {@code keys} is simply returned.
+	 * <p/>
+	 * Otherwise, a new typed array is created and the contents copied from {@code keys} to this new array.  If
+	 * key {@linkplain org.hibernate.cfg.AvailableSettings#JPA_LOAD_BY_ID_COMPLIANCE coercion} is enabled, the
+	 * values will be coerced to the key type.
+	 *
+	 * @param keys The keys to normalize
+	 * @param keyPart The ModelPart describing the key
+	 *
+	 * @param <K> The key type
+	 */
+	public static <K> K[] normalizeKeys(
+			K[] keys,
+			BasicValuedModelPart keyPart,
+			SharedSessionContractImplementor session,
+			SessionFactoryImplementor sessionFactory) {
+		assert keys.getClass().isArray();
+
+		//noinspection unchecked
+		final JavaType<K> keyJavaType = (JavaType<K>) keyPart.getJavaType();
+		final Class<K> keyClass = keyJavaType.getJavaTypeClass();
+
+		if ( keys.getClass().getComponentType().equals( keyClass ) ) {
+			return keys;
+		}
+
+		final K[] typedArray = createTypedArray( keyClass, keys.length );
+		final boolean coerce = !sessionFactory.getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
+		if ( !coerce ) {
+			System.arraycopy( keys, 0, typedArray, 0, keys.length );
+		}
+		else {
+			for ( int i = 0; i < keys.length; i++ ) {
+				typedArray[i] = keyJavaType.coerce( keys[i], session );
+			}
+		}
+		return typedArray;
+	}
+
+	/**
+	 * Creates a typed array, as opposed to a generic {@code Object[]} that holds the typed values
+	 *
+	 * @param elementClass The type of the array elements.  See {@link Class#getComponentType()}
+	 * @param length The length to which the array should be created.  This is usually zero for Hibernate uses
+	 */
+	public static <X> X[] createTypedArray(Class<X> elementClass, @SuppressWarnings("SameParameterValue") int length) {
+		//noinspection unchecked
+		return (X[]) Array.newInstance( elementClass, length );
+	}
+
+	/**
+	 * Load one or more instances of a model part (an entity or collection)
+	 * based on a SQL ARRAY parameter to specify the keys (as opposed to the
+	 * more traditional SQL IN predicate approach).
+	 *
+	 * @param <R> The type of the model part to load
+	 * @param <K> The type of the keys
+	 */
+	public static <R,K> List<R> loadByArrayParameter(
+			K[] idsToInitialize,
+			SelectStatement sqlAst,
+			JdbcOperationQuerySelect jdbcOperation,
+			JdbcParameter jdbcParameter,
+			JdbcMapping arrayJdbcMapping,
+			Object entityId,
+			Object entityInstance,
+			LockOptions lockOptions,
+			Boolean readOnly,
+			SharedSessionContractImplementor session) {
+		assert jdbcOperation != null;
+		assert jdbcParameter != null;
+
+		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl( 1);
+		jdbcParameterBindings.addBinding(
+				jdbcParameter,
+				new JdbcParameterBindingImpl( arrayJdbcMapping, idsToInitialize )
+		);
+
+		final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
+				session.getPersistenceContext().getBatchFetchQueue(),
+				sqlAst,
+				Collections.singletonList( jdbcParameter ),
+				jdbcParameterBindings
+		);
+
+		return session.getJdbcServices().getJdbcSelectExecutor().list(
+				jdbcOperation,
+				jdbcParameterBindings,
+				new SingleIdExecutionContext(
+						entityId,
+						entityInstance,
+						readOnly,
+						lockOptions,
+						subSelectFetchableKeysHandler,
+						session
+				),
+				RowTransformerStandardImpl.instance(),
+				ListResultsConsumer.UniqueSemantic.FILTER
+		);
+	}
 }

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/LoaderSelectBuilder.java

@@ -40,6 +40,7 @@ import org.hibernate.metamodel.mapping.NaturalIdMapping;
 import org.hibernate.metamodel.mapping.NonAggregatedIdentifierMapping;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.metamodel.mapping.Restrictable;
+import org.hibernate.metamodel.mapping.SelectableMapping;
 import org.hibernate.metamodel.mapping.internal.EmbeddedAttributeMapping;
 import org.hibernate.metamodel.mapping.internal.SimpleForeignKeyDescriptor;
 import org.hibernate.metamodel.mapping.internal.ToOneAttributeMapping;
@@ -65,6 +66,7 @@ import org.hibernate.sql.ast.tree.from.TableGroupJoin;
 import org.hibernate.sql.ast.tree.from.TableGroupJoinProducer;
 import org.hibernate.sql.ast.tree.from.TableReference;
 import org.hibernate.sql.ast.tree.predicate.ComparisonPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.InListPredicate;
 import org.hibernate.sql.ast.tree.predicate.InSubQueryPredicate;
 import org.hibernate.sql.ast.tree.select.QueryPart;
@@ -99,13 +101,12 @@ public class LoaderSelectBuilder {
 	private static final Logger log = Logger.getLogger( LoaderSelectBuilder.class );
 
 	/**
-	 * Create an SQL AST select-statement for a select by unique key based on matching one-or-more keys
+	 * Create an SQL AST select-statement for loading by unique key
 	 *
 	 * @param loadable The root Loadable
 	 * @param partsToSelect Parts of the Loadable to select.  Null/empty indicates to select the Loadable itself
 	 * @param restrictedPart Part to base the where-clause restriction on
 	 * @param cachedDomainResult DomainResult to be used.  Null indicates to generate the DomainResult
-	 * @param numberOfKeysToLoad How many keys should be accounted for in the where-clause restriction?
 	 * @param loadQueryInfluencers Any influencers (entity graph, fetch profile) to account for
 	 * @param lockOptions Pessimistic lock options to apply
 	 * @param jdbcParameterConsumer Consumer for all JdbcParameter references created
@@ -116,7 +117,6 @@ public class LoaderSelectBuilder {
 			List<? extends ModelPart> partsToSelect,
 			ModelPart restrictedPart,
 			DomainResult<?> cachedDomainResult,
-			int numberOfKeysToLoad,
 			LoadQueryInfluencers loadQueryInfluencers,
 			LockOptions lockOptions,
 			Consumer<JdbcParameter> jdbcParameterConsumer,
@@ -127,7 +127,7 @@ public class LoaderSelectBuilder {
 				partsToSelect,
 				singletonList( restrictedPart ),
 				cachedDomainResult,
-				numberOfKeysToLoad,
+				1,
 				loadQueryInfluencers,
 				lockOptions,
 				determineGraphTraversalState( loadQueryInfluencers ),
@@ -138,6 +138,86 @@ public class LoaderSelectBuilder {
 		return process.generateSelect();
 	}
 
+	/**
+	 * Create a select-statement (SQL AST) for loading by multiple keys using a single SQL ARRAY parameter
+	 */
+	public static SelectStatement createSelectBySingleArrayParameter(
+			Loadable loadable,
+			BasicValuedModelPart restrictedPart,
+			LoadQueryInfluencers influencers,
+			LockOptions lockOptions,
+			JdbcParameter jdbcArrayParameter,
+			SessionFactoryImplementor sessionFactory) {
+		final LoaderSelectBuilder builder = new LoaderSelectBuilder(
+				sessionFactory,
+				loadable,
+				null,
+				singletonList( restrictedPart ),
+				null,
+				-1,
+				influencers,
+				lockOptions,
+				determineGraphTraversalState( influencers ),
+				true,
+				null
+		);
+
+		final QuerySpec rootQuerySpec = new QuerySpec( true );
+		final LoaderSqlAstCreationState sqlAstCreationState = builder.createSqlAstCreationState( rootQuerySpec );
+
+		final NavigablePath rootNavigablePath = new NavigablePath( loadable.getRootPathName() );
+		final TableGroup rootTableGroup = builder.buildRootTableGroup( rootNavigablePath, rootQuerySpec, sqlAstCreationState );
+
+		final DomainResult<?> domainResult = loadable.createDomainResult(
+				rootNavigablePath,
+				rootTableGroup,
+				null,
+				sqlAstCreationState
+		);
+
+		final List<DomainResult<?>> domainResults = singletonList( domainResult );
+
+		applyArrayParamRestriction(
+				rootQuerySpec,
+				rootNavigablePath,
+				rootTableGroup,
+				restrictedPart,
+				jdbcArrayParameter,
+				sqlAstCreationState
+		);
+
+
+		if ( loadable instanceof PluralAttributeMapping ) {
+			final PluralAttributeMapping pluralAttributeMapping = (PluralAttributeMapping) loadable;
+			builder.applyFiltering( rootQuerySpec, rootTableGroup, pluralAttributeMapping, sqlAstCreationState );
+			builder.applyOrdering( rootQuerySpec, rootTableGroup, pluralAttributeMapping, sqlAstCreationState );
+		}
+		else {
+			builder.applyFiltering( rootQuerySpec, rootTableGroup, (Restrictable) loadable, sqlAstCreationState );
+		}
+
+		return new SelectStatement( rootQuerySpec, domainResults );
+	}
+
+	private static void applyArrayParamRestriction(
+			QuerySpec rootQuerySpec,
+			NavigablePath rootNavigablePath,
+			TableGroup rootTableGroup,
+			BasicValuedModelPart restrictedPart,
+			JdbcParameter jdbcArrayParameter,
+			LoaderSqlAstCreationState sqlAstCreationState) {
+		final SqlExpressionResolver sqlExpressionResolver = sqlAstCreationState.getSqlExpressionResolver();
+		final SelectableMapping restrictedPartMapping = restrictedPart.getSelectable( 0 );
+		final NavigablePath restrictionPath = rootNavigablePath.append( restrictedPart.getNavigableRole().getNavigableName() );
+		final TableReference tableReference = rootTableGroup.resolveTableReference( restrictionPath, restrictedPartMapping.getContainingTableExpression() );
+		final ColumnReference columnRef = (ColumnReference) sqlExpressionResolver.resolveSqlExpression(
+				tableReference,
+				restrictedPartMapping
+		);
+
+		rootQuerySpec.applyPredicate( new InArrayPredicate( columnRef, jdbcArrayParameter ) );
+	}
+
 	/**
 	 * Create an SQL AST select-statement based on matching one-or-more keys
 	 *
@@ -372,90 +452,24 @@ public class LoaderSelectBuilder {
 		final NavigablePath rootNavigablePath = new NavigablePath( loadable.getRootPathName() );
 
 		final QuerySpec rootQuerySpec = new QuerySpec( true );
+		final LoaderSqlAstCreationState sqlAstCreationState = createSqlAstCreationState( rootQuerySpec );
+
+		final TableGroup rootTableGroup = buildRootTableGroup( rootNavigablePath, rootQuerySpec, sqlAstCreationState );
+
 		final List<DomainResult<?>> domainResults;
-
-		final LoaderSqlAstCreationState sqlAstCreationState = new LoaderSqlAstCreationState(
-				rootQuerySpec,
-				new SqlAliasBaseManager(),
-				new SimpleFromClauseAccessImpl(),
-				lockOptions,
-				this::visitFetches,
-				forceIdentifierSelection,
-				loadQueryInfluencers,
-				creationContext
-		);
-
-		final TableGroup rootTableGroup = loadable.createRootTableGroup(
-				true,
-				rootNavigablePath,
-				null,
-				null,
-				() -> rootQuerySpec::applyPredicate,
-				sqlAstCreationState
-		);
-
-		rootQuerySpec.getFromClause().addRoot( rootTableGroup );
-		sqlAstCreationState.getFromClauseAccess().registerTableGroup( rootNavigablePath, rootTableGroup );
-		registerPluralTableGroupParts( sqlAstCreationState.getFromClauseAccess(), rootTableGroup );
-
 		if ( partsToSelect != null && !partsToSelect.isEmpty() ) {
-			domainResults = new ArrayList<>( partsToSelect.size() );
+			domainResults = buildRequestedDomainResults( rootNavigablePath, sqlAstCreationState, rootTableGroup );
-			for ( ModelPart part : partsToSelect ) {
+		}
-				final NavigablePath navigablePath = rootNavigablePath.append( part.getPartName() );
+		else if ( this.cachedDomainResult != null ) {
-				final TableGroup tableGroup;
+			domainResults = singletonList( this.cachedDomainResult );
-				if ( part instanceof TableGroupJoinProducer ) {
-					final TableGroupJoinProducer tableGroupJoinProducer = (TableGroupJoinProducer) part;
-					final TableGroupJoin tableGroupJoin = tableGroupJoinProducer.createTableGroupJoin(
-							navigablePath,
-							rootTableGroup,
-							null,
-							null,
-							SqlAstJoinType.LEFT,
-							true,
-							false,
-							sqlAstCreationState
-					);
-					rootTableGroup.addTableGroupJoin( tableGroupJoin );
-					tableGroup = tableGroupJoin.getJoinedGroup();
-					sqlAstCreationState.getFromClauseAccess().registerTableGroup( navigablePath, tableGroup );
-					registerPluralTableGroupParts( sqlAstCreationState.getFromClauseAccess(), tableGroup );
-				}
-				else {
-					tableGroup = rootTableGroup;
-				}
-				domainResults.add(
-						part.createDomainResult(
-								navigablePath,
-								tableGroup,
-								null,
-								sqlAstCreationState
-						)
-				);
-			}
 		}
 		else {
-			// use the one passed to the constructor or create one (maybe always create and pass?)
+			final DomainResult<?> domainResult = loadable.createDomainResult(
-			//		allows re-use as they can be re-used to save on memory - they
+					rootNavigablePath,
-			//		do not share state between
+					rootTableGroup,
-
+					null,
-			//noinspection rawtypes
+					sqlAstCreationState
-			final DomainResult domainResult;
+			);
-
-			if ( this.cachedDomainResult != null ) {
-				// used the one passed to the constructor
-				domainResult = this.cachedDomainResult;
-			}
-			else {
-				// create one
-				domainResult = loadable.createDomainResult(
-						rootNavigablePath,
-						rootTableGroup,
-						null,
-						sqlAstCreationState
-				);
-			}
-
-			//noinspection unchecked
 			domainResults = singletonList( domainResult );
 		}
 
@@ -485,19 +499,87 @@ public class LoaderSelectBuilder {
 		return new SelectStatement( rootQuerySpec, domainResults );
 	}
 
+	private List<DomainResult<?>> buildRequestedDomainResults(NavigablePath rootNavigablePath, LoaderSqlAstCreationState sqlAstCreationState, TableGroup rootTableGroup) {
+		final List<DomainResult<?>> domainResults;
+		domainResults = new ArrayList<>( partsToSelect.size() );
+		for ( ModelPart part : partsToSelect ) {
+			final NavigablePath navigablePath = rootNavigablePath.append( part.getPartName() );
+			final TableGroup tableGroup;
+			if ( part instanceof TableGroupJoinProducer ) {
+				final TableGroupJoinProducer tableGroupJoinProducer = (TableGroupJoinProducer) part;
+				final TableGroupJoin tableGroupJoin = tableGroupJoinProducer.createTableGroupJoin(
+						navigablePath,
+						rootTableGroup,
+						null,
+						null,
+						SqlAstJoinType.LEFT,
+						true,
+						false,
+						sqlAstCreationState
+				);
+				rootTableGroup.addTableGroupJoin( tableGroupJoin );
+				tableGroup = tableGroupJoin.getJoinedGroup();
+				sqlAstCreationState.getFromClauseAccess().registerTableGroup( navigablePath, tableGroup );
+				registerPluralTableGroupParts( sqlAstCreationState.getFromClauseAccess(), tableGroup );
+			}
+			else {
+				tableGroup = rootTableGroup;
+			}
+			domainResults.add(
+					part.createDomainResult(
+							navigablePath,
+							tableGroup,
+							null,
+							sqlAstCreationState
+					)
+			);
+		}
+		return domainResults;
+	}
+
+	private TableGroup buildRootTableGroup(NavigablePath rootNavigablePath, QuerySpec rootQuerySpec, LoaderSqlAstCreationState sqlAstCreationState) {
+		final TableGroup rootTableGroup = loadable.createRootTableGroup(
+				true,
+				rootNavigablePath,
+				null,
+				null,
+				() -> rootQuerySpec::applyPredicate,
+				sqlAstCreationState
+		);
+
+		rootQuerySpec.getFromClause().addRoot( rootTableGroup );
+		sqlAstCreationState.getFromClauseAccess().registerTableGroup( rootNavigablePath, rootTableGroup );
+		registerPluralTableGroupParts( sqlAstCreationState.getFromClauseAccess(), rootTableGroup );
+		return rootTableGroup;
+	}
+
+	private LoaderSqlAstCreationState createSqlAstCreationState(QuerySpec rootQuerySpec) {
+		final LoaderSqlAstCreationState sqlAstCreationState = new LoaderSqlAstCreationState(
+				rootQuerySpec,
+				new SqlAliasBaseManager(),
+				new SimpleFromClauseAccessImpl(),
+				lockOptions,
+				this::visitFetches,
+				forceIdentifierSelection,
+				loadQueryInfluencers,
+				creationContext
+		);
+		return sqlAstCreationState;
+	}
+
 	private void applyRestriction(
 			QuerySpec rootQuerySpec,
 			NavigablePath rootNavigablePath,
 			TableGroup rootTableGroup,
-			ModelPart modelPart,
+			ModelPart restrictedPart,
 			int numberColumns,
 			Consumer<JdbcParameter> jdbcParameterConsumer,
 			LoaderSqlAstCreationState sqlAstCreationState) {
 		final SqlExpressionResolver sqlExpressionResolver = sqlAstCreationState.getSqlExpressionResolver();
-		final NavigablePath navigablePath = rootNavigablePath.append( modelPart.getNavigableRole().getNavigableName() );
+		final NavigablePath navigablePath = rootNavigablePath.append( restrictedPart.getNavigableRole().getNavigableName() );
 
 		if ( numberColumns == 1 ) {
-			modelPart.forEachSelectable(
+			restrictedPart.forEachSelectable(
 					(columnIndex, selection) -> {
 						final TableReference tableReference = rootTableGroup.resolveTableReference(
 								navigablePath, selection.getContainingTableExpression() );
@@ -532,7 +614,7 @@ public class LoaderSelectBuilder {
 		else {
 			final List<ColumnReference> columnReferences = new ArrayList<>( numberColumns );
 
-			modelPart.forEachSelectable(
+			restrictedPart.forEachSelectable(
 					(columnIndex, selection) -> {
 						final TableReference tableReference = rootTableGroup.resolveTableReference( navigablePath, selection.getContainingTableExpression() );
 						columnReferences.add(
@@ -544,7 +626,7 @@ public class LoaderSelectBuilder {
 					}
 			);
 
-			final SqlTuple tuple = new SqlTuple( columnReferences, modelPart );
+			final SqlTuple tuple = new SqlTuple( columnReferences, restrictedPart );
 			final InListPredicate predicate = new InListPredicate( tuple );
 
 			for ( int i = 0; i < numberOfKeysToLoad; i++ ) {
@@ -555,7 +637,7 @@ public class LoaderSelectBuilder {
 					jdbcParameterConsumer.accept( jdbcParameter );
 					tupleParams.add( jdbcParameter );
 				}
-				final SqlTuple paramTuple = new SqlTuple( tupleParams, modelPart );
+				final SqlTuple paramTuple = new SqlTuple( tupleParams, restrictedPart );
 				predicate.addExpression( paramTuple );
 			}
 
@@ -974,18 +1056,7 @@ public class LoaderSelectBuilder {
 				creationContext
 		);
 
-		final TableGroup rootTableGroup = loadable.createRootTableGroup(
+		final TableGroup rootTableGroup = buildRootTableGroup( rootNavigablePath, rootQuerySpec, sqlAstCreationState );
-				true,
-				rootNavigablePath,
-				null,
-				null,
-				() -> rootQuerySpec::applyPredicate,
-				sqlAstCreationState
-		);
-
-		rootQuerySpec.getFromClause().addRoot( rootTableGroup );
-		sqlAstCreationState.getFromClauseAccess().registerTableGroup( rootNavigablePath, rootTableGroup );
-		registerPluralTableGroupParts( sqlAstCreationState.getFromClauseAccess(), rootTableGroup );
 
 		// generate and apply the restriction
 		applySubSelectRestriction(

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiIdEntityLoaderArrayParam.java

@@ -0,0 +1,409 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.hibernate.LockMode;
+import org.hibernate.LockOptions;
+import org.hibernate.engine.internal.BatchFetchQueueHelper;
+import org.hibernate.engine.spi.BatchFetchQueue;
+import org.hibernate.engine.spi.EntityEntry;
+import org.hibernate.engine.spi.EntityKey;
+import org.hibernate.engine.spi.PersistenceContext;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SubselectFetch;
+import org.hibernate.event.spi.EventSource;
+import org.hibernate.event.spi.LoadEvent;
+import org.hibernate.event.spi.LoadEventListener;
+import org.hibernate.internal.util.collections.CollectionHelper;
+import org.hibernate.loader.ast.internal.CacheEntityLoaderHelper.PersistenceContextEntry;
+import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
+import org.hibernate.loader.ast.spi.SqlArrayMultiKeyLoader;
+import org.hibernate.metamodel.mapping.BasicEntityIdentifierMapping;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.metamodel.mapping.JdbcMapping;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
+import org.hibernate.sql.exec.internal.JdbcParameterImpl;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
+import org.hibernate.sql.results.spi.ListResultsConsumer;
+import org.hibernate.type.BasicType;
+import org.hibernate.type.BasicTypeRegistry;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+import static org.hibernate.internal.util.collections.CollectionHelper.isEmpty;
+
+/**
+ * @author Steve Ebersole
+ */
+public class MultiIdEntityLoaderArrayParam<E> extends AbstractMultiIdEntityLoader<E> implements SqlArrayMultiKeyLoader, Preparable {
+	private JdbcMapping arrayJdbcMapping;
+	private JdbcParameter jdbcParameter;
+
+	public MultiIdEntityLoaderArrayParam(EntityMappingType entityDescriptor, SessionFactoryImplementor sessionFactory) {
+		super( entityDescriptor, sessionFactory );
+	}
+
+	@Override
+	public BasicEntityIdentifierMapping getIdentifierMapping() {
+		return (BasicEntityIdentifierMapping) super.getIdentifierMapping();
+	}
+
+	@Override
+	protected <K> List<E> performOrderedMultiLoad(K[] ids, MultiIdLoadOptions loadOptions, EventSource session) {
+		if ( MultiKeyLoadLogging.MULTI_KEY_LOAD_TRACE_ENABLED ) {
+			MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER.tracef(
+					"MultiIdEntityLoaderArrayParam#performOrderedMultiLoad - %s",
+					getLoadable().getEntityName()
+			);
+		}
+
+		final boolean coerce = !getSessionFactory().getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
+		final LockOptions lockOptions = (loadOptions.getLockOptions() == null)
+				? new LockOptions( LockMode.NONE )
+				: loadOptions.getLockOptions();
+
+		final List<Object> result = CollectionHelper.arrayList( ids.length );
+		List<Object> idsToLoadFromDatabase = null;
+		List<Integer> idsToLoadFromDatabaseResultIndexes = null;
+
+		for ( int i = 0; i < ids.length; i++ ) {
+			final Object id;
+			if ( coerce ) {
+				id = getLoadable().getIdentifierMapping().getJavaType().coerce( ids[ i ], session );
+			}
+			else {
+				id = ids[ i ];
+			}
+
+			final EntityKey entityKey = new EntityKey( id, getLoadable().getEntityPersister() );
+
+			if ( loadOptions.isSessionCheckingEnabled() || loadOptions.isSecondLevelCacheCheckingEnabled() ) {
+				LoadEvent loadEvent = new LoadEvent(
+						id,
+						getLoadable().getJavaType().getJavaTypeClass().getName(),
+						lockOptions,
+						session,
+						LoaderHelper.getReadOnlyFromLoadQueryInfluencers(session)
+				);
+
+				Object managedEntity = null;
+
+				if ( loadOptions.isSessionCheckingEnabled() ) {
+					// look for it in the Session first
+					final PersistenceContextEntry persistenceContextEntry = CacheEntityLoaderHelper.loadFromSessionCacheStatic(
+							loadEvent,
+							entityKey,
+							LoadEventListener.GET
+					);
+					managedEntity = persistenceContextEntry.getEntity();
+
+					if ( managedEntity != null
+							&& !loadOptions.isReturnOfDeletedEntitiesEnabled()
+							&& !persistenceContextEntry.isManaged() ) {
+						// put a null in the result
+						result.add( i, null );
+						continue;
+					}
+				}
+
+				if ( managedEntity == null && loadOptions.isSecondLevelCacheCheckingEnabled() ) {
+					// look for it in the SessionFactory
+					managedEntity = CacheEntityLoaderHelper.INSTANCE.loadFromSecondLevelCache(
+							loadEvent,
+							getLoadable().getEntityPersister(),
+							entityKey
+					);
+				}
+
+				if ( managedEntity != null ) {
+					result.add( i, managedEntity );
+					continue;
+				}
+			}
+
+			// if we did not hit any of the continues above, then we need to batch
+			// load the entity state.
+			if ( idsToLoadFromDatabase == null ) {
+				idsToLoadFromDatabase = new ArrayList<>();
+				idsToLoadFromDatabaseResultIndexes = new ArrayList<>();
+			}
+			// hold its place in the result with the EntityKey, we'll come back to it later
+			result.add( i, entityKey );
+			idsToLoadFromDatabase.add( id );
+			idsToLoadFromDatabaseResultIndexes.add( i );
+		}
+
+		if ( idsToLoadFromDatabase == null ) {
+			// all the given ids were already associated with the Session
+			//noinspection unchecked
+			return (List<E>) result;
+		}
+
+		final SelectStatement sqlAst = LoaderSelectBuilder.createSelectBySingleArrayParameter(
+				getLoadable(),
+				getIdentifierMapping(),
+				session.getLoadQueryInfluencers(),
+				lockOptions,
+				jdbcParameter,
+				getSessionFactory()
+		);
+		final JdbcOperationQuerySelect jdbcSelectOperation = getSessionFactory().getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( getSessionFactory(), sqlAst )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+
+		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl(1);
+		jdbcParameterBindings.addBinding(
+				jdbcParameter,
+				new JdbcParameterBindingImpl( arrayJdbcMapping, idsToLoadFromDatabase.toArray( createTypedArray(0 ) ) )
+		);
+
+		final PersistenceContext persistenceContext = session.getPersistenceContext();
+		final BatchFetchQueue batchFetchQueue = persistenceContext.getBatchFetchQueue();
+
+		final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
+				batchFetchQueue,
+				sqlAst,
+				Collections.singletonList( jdbcParameter ),
+				jdbcParameterBindings
+		);
+
+		session.getJdbcServices().getJdbcSelectExecutor().list(
+				jdbcSelectOperation,
+				jdbcParameterBindings,
+				new ExecutionContextWithSubselectFetchHandler( session, subSelectFetchableKeysHandler ),
+				RowTransformerStandardImpl.instance(),
+				ListResultsConsumer.UniqueSemantic.FILTER
+		);
+
+		for ( int i = 0; i < idsToLoadFromDatabaseResultIndexes.size(); i++ ) {
+			final Integer resultIndex = idsToLoadFromDatabaseResultIndexes.get(i);
+
+			// the element value at this position in the result List should be
+			// the EntityKey for that entity - reuse it
+			final EntityKey entityKey = (EntityKey) result.get( resultIndex );
+			BatchFetchQueueHelper.removeBatchLoadableEntityKey( entityKey, session );
+			Object entity = persistenceContext.getEntity( entityKey );
+			if ( entity != null && !loadOptions.isReturnOfDeletedEntitiesEnabled() ) {
+				// make sure it is not DELETED
+				final EntityEntry entry = persistenceContext.getEntry( entity );
+				if ( entry.getStatus().isDeletedOrGone() ) {
+					// the entity is locally deleted, and the options ask that we not return such entities...
+					entity = null;
+				}
+			}
+			result.set( resultIndex, entity );
+		}
+
+		//noinspection unchecked
+		return (List<E>) result;
+	}
+
+
+	@Override
+	protected <K> List<E> performUnorderedMultiLoad(
+			K[] ids,
+			MultiIdLoadOptions loadOptions,
+			EventSource session) {
+		if ( MultiKeyLoadLogging.MULTI_KEY_LOAD_TRACE_ENABLED ) {
+			MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER.tracef(
+					"MultiIdEntityLoaderArrayParam#performUnorderedMultiLoad - %s",
+					getLoadable().getEntityName()
+			);
+		}
+
+		final List<E> result = CollectionHelper.arrayList( ids.length );
+		final LockOptions lockOptions = (loadOptions.getLockOptions() == null)
+				? new LockOptions( LockMode.NONE )
+				: loadOptions.getLockOptions();
+
+		//noinspection unchecked
+		final K[] idsToLoadFromDatabase = processResolvableEntities(
+				ids,
+				(index, entityKey, resolvedEntity) -> result.add( (E) resolvedEntity ),
+				loadOptions,
+				lockOptions,
+				session
+		);
+
+		if ( idsToLoadFromDatabase == null ) {
+			// all the given ids were already associated with the Session
+			return result;
+		}
+
+		final SelectStatement sqlAst = LoaderSelectBuilder.createSelectBySingleArrayParameter(
+				getLoadable(),
+				getIdentifierMapping(),
+				session.getLoadQueryInfluencers(),
+				lockOptions,
+				jdbcParameter,
+				getSessionFactory()
+		);
+		final JdbcOperationQuerySelect jdbcSelectOperation = getSessionFactory().getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( getSessionFactory(), sqlAst )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+
+		final List<E> databaseResults = LoaderHelper.loadByArrayParameter(
+				idsToLoadFromDatabase,
+				sqlAst,
+				jdbcSelectOperation,
+				jdbcParameter,
+				arrayJdbcMapping,
+				null,
+				null,
+				lockOptions,
+				session.isDefaultReadOnly(),
+				session
+		);
+		result.addAll( databaseResults );
+
+		//noinspection ForLoopReplaceableByForEach
+		for ( int i = 0; i < idsToLoadFromDatabase.length; i++ ) {
+			final Object id = idsToLoadFromDatabase[i];
+			if ( id == null ) {
+				// skip any of the null padded ids
+				//		- actually we could probably even break here
+				continue;
+			}
+			// found or not, remove the key from the batch-fetch queue
+			BatchFetchQueueHelper.removeBatchLoadableEntityKey( id, getLoadable(), session );
+		}
+
+		return result;
+	}
+	public interface ResolutionConsumer<T> {
+		void consume(int position, EntityKey entityKey, T resolvedRef);
+	}
+
+	protected final <R,K> K[] processResolvableEntities(
+			K[] ids,
+			ResolutionConsumer<R> resolutionConsumer,
+			@NonNull MultiIdLoadOptions loadOptions,
+			@NonNull LockOptions lockOptions,
+			EventSource session) {
+		if ( !loadOptions.isSessionCheckingEnabled()
+				&& !loadOptions.isSecondLevelCacheCheckingEnabled() ) {
+			// we'll load all of them from the database
+			return ids;
+		}
+
+		final boolean coerce = !getSessionFactory().getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
+
+		boolean foundAnyResolvedEntities = false;
+		List<K> nonResolvedIds = null;
+
+		for ( int i = 0; i < ids.length; i++ ) {
+			final Object id;
+			if ( coerce ) {
+				//noinspection unchecked
+				id = (K) getLoadable().getIdentifierMapping().getJavaType().coerce( ids[i], session );
+			}
+			else {
+				id = ids[i];
+			}
+
+			final EntityKey entityKey = new EntityKey( id, getLoadable().getEntityPersister() );
+			final LoadEvent loadEvent = new LoadEvent(
+					id,
+					getLoadable().getJavaType().getJavaTypeClass().getName(),
+					lockOptions,
+					session,
+					LoaderHelper.getReadOnlyFromLoadQueryInfluencers( session )
+			);
+
+			Object resolvedEntity = null;
+
+			// look for it in the Session first
+			final PersistenceContextEntry persistenceContextEntry = CacheEntityLoaderHelper.loadFromSessionCacheStatic(
+					loadEvent,
+					entityKey,
+					LoadEventListener.GET
+			);
+			if ( loadOptions.isSessionCheckingEnabled() ) {
+				resolvedEntity = persistenceContextEntry.getEntity();
+
+				if ( resolvedEntity != null
+						&& !loadOptions.isReturnOfDeletedEntitiesEnabled()
+						&& !persistenceContextEntry.isManaged() ) {
+					foundAnyResolvedEntities = true;
+					resolutionConsumer.consume( i, entityKey, null );
+					continue;
+				}
+			}
+
+			if ( resolvedEntity == null && loadOptions.isSecondLevelCacheCheckingEnabled() ) {
+				resolvedEntity = CacheEntityLoaderHelper.INSTANCE.loadFromSecondLevelCache(
+						loadEvent,
+						getLoadable().getEntityPersister(),
+						entityKey
+				);
+			}
+
+			if ( resolvedEntity != null ) {
+				foundAnyResolvedEntities = true;
+
+				//noinspection unchecked
+				resolutionConsumer.consume( i, entityKey, (R) resolvedEntity);
+			}
+			else {
+				if ( nonResolvedIds == null ) {
+					nonResolvedIds = new ArrayList<>();
+				}
+				//noinspection unchecked,CastCanBeRemovedNarrowingVariableType
+				nonResolvedIds.add( (K) id );
+			}
+		}
+
+		if ( foundAnyResolvedEntities ) {
+			if ( isEmpty( nonResolvedIds ) ) {
+				// all the given ids were already associated with the Session
+				return null;
+			}
+
+			return nonResolvedIds.toArray( createTypedArray(0) );
+		}
+
+		return ids;
+	}
+
+	private  <X> X[] createTypedArray(@SuppressWarnings("SameParameterValue") int length) {
+		//noinspection unchecked
+		return (X[]) Array.newInstance( getIdentifierMapping().getJavaType().getJavaTypeClass(), length );
+	}
+
+	@Override
+	public void prepare() {
+		super.prepare();
+
+		final Class<?> arrayClass = createTypedArray( 0 ).getClass();
+
+		final BasicTypeRegistry basicTypeRegistry = getSessionFactory().getTypeConfiguration().getBasicTypeRegistry();
+		final BasicType<?> arrayBasicType = basicTypeRegistry.getRegisteredType( arrayClass );
+
+		arrayJdbcMapping = MultiKeyLoadHelper.resolveArrayJdbcMapping(
+				arrayBasicType,
+				getIdentifierMapping().getJdbcMapping(),
+				arrayClass,
+				getSessionFactory()
+		);
+		jdbcParameter = new JdbcParameterImpl( arrayJdbcMapping );
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiIdEntityLoaderStandard.java

@@ -19,7 +19,6 @@ import org.hibernate.engine.jdbc.env.spi.JdbcEnvironment;
 import org.hibernate.engine.jdbc.spi.JdbcServices;
 import org.hibernate.engine.spi.EntityEntry;
 import org.hibernate.engine.spi.EntityKey;
-import org.hibernate.engine.spi.LoadQueryInfluencers;
 import org.hibernate.engine.spi.PersistenceContext;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
@@ -28,10 +27,8 @@ import org.hibernate.event.spi.EventSource;
 import org.hibernate.event.spi.LoadEvent;
 import org.hibernate.event.spi.LoadEventListener;
 import org.hibernate.internal.util.collections.CollectionHelper;
-import org.hibernate.loader.ast.spi.MultiIdEntityLoader;
 import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
 import org.hibernate.mapping.PersistentClass;
-import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.query.spi.QueryOptions;
 import org.hibernate.sql.ast.SqlAstTranslatorFactory;
@@ -46,55 +43,37 @@ import org.hibernate.sql.results.spi.ListResultsConsumer;
 import org.jboss.logging.Logger;
 
 /**
+ * Standard MultiIdEntityLoader
+ *
  * @author Steve Ebersole
  */
-public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
+public class MultiIdEntityLoaderStandard<T> extends AbstractMultiIdEntityLoader<T> {
-	private static final Logger log = Logger.getLogger( MultiIdLoaderStandard.class );
+	private static final Logger log = Logger.getLogger( MultiIdEntityLoaderStandard.class );
-
-	private final EntityPersister entityDescriptor;
-	private final SessionFactoryImplementor sessionFactory;
 
 	private final int idJdbcTypeCount;
 
-	public MultiIdLoaderStandard(
+	public MultiIdEntityLoaderStandard(
 			EntityPersister entityDescriptor,
 			PersistentClass bootDescriptor,
 			SessionFactoryImplementor sessionFactory) {
-		this.entityDescriptor = entityDescriptor;
+		super( entityDescriptor, sessionFactory );
 		this.idJdbcTypeCount = bootDescriptor.getIdentifier().getColumnSpan();
-		this.sessionFactory = sessionFactory;
 
 		assert idJdbcTypeCount > 0;
 	}
 
 	@Override
-	public EntityMappingType getLoadable() {
+	protected List<T> performOrderedMultiLoad(
-		return entityDescriptor;
-	}
-
-	@Override
-	public List<T> load(Object[] ids, MultiIdLoadOptions loadOptions, EventSource session) {
-		assert ids != null;
-
-		if ( loadOptions.isOrderReturnEnabled() ) {
-			return performOrderedMultiLoad( ids, session, loadOptions );
-		}
-		else {
-			return performUnorderedMultiLoad( ids, session, loadOptions );
-		}
-	}
-
-	private List<T> performOrderedMultiLoad(
 			Object[] ids,
-			EventSource session,
+			MultiIdLoadOptions loadOptions,
-			MultiIdLoadOptions loadOptions) {
+			EventSource session) {
 		if ( log.isTraceEnabled() ) {
-			log.tracef( "#performOrderedMultiLoad(`%s`, ..)", entityDescriptor.getEntityName() );
+			log.tracef( "#performOrderedMultiLoad(`%s`, ..)", getLoadable().getEntityName() );
 		}
 
 		assert loadOptions.isOrderReturnEnabled();
 
-		final JdbcEnvironment jdbcEnvironment = sessionFactory.getJdbcServices().getJdbcEnvironment();
+		final JdbcEnvironment jdbcEnvironment = getSessionFactory().getJdbcServices().getJdbcEnvironment();
 		final Dialect dialect = jdbcEnvironment.getDialect();
 
 		final List<Object> result = CollectionHelper.arrayList( ids.length );
@@ -108,34 +87,34 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 			maxBatchSize = loadOptions.getBatchSize();
 		}
 		else {
-			maxBatchSize = dialect.getDefaultBatchLoadSizingStrategy().determineOptimalBatchLoadSize(
+			maxBatchSize = dialect.getBatchLoadSizingStrategy().determineOptimalBatchLoadSize(
 					idJdbcTypeCount,
 					ids.length,
-					sessionFactory.getSessionFactoryOptions().inClauseParameterPaddingEnabled()
+					getSessionFactory().getSessionFactoryOptions().inClauseParameterPaddingEnabled()
 			);
 		}
 
 		final List<Object> idsInBatch = new ArrayList<>();
 		final List<Integer> elementPositionsLoadedByBatch = new ArrayList<>();
 
-		final boolean coerce = !sessionFactory.getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
+		final boolean coerce = !getSessionFactory().getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
 		for ( int i = 0; i < ids.length; i++ ) {
 			final Object id;
 			if ( coerce ) {
-				id = entityDescriptor.getIdentifierMapping().getJavaType().coerce( ids[i], session );
+				id = getLoadable().getIdentifierMapping().getJavaType().coerce( ids[i], session );
 			}
 			else {
 				id = ids[i];
 			}
-			final EntityKey entityKey = new EntityKey( id, entityDescriptor );
+			final EntityKey entityKey = new EntityKey( id, getLoadable().getEntityPersister() );
 
 			if ( loadOptions.isSessionCheckingEnabled() || loadOptions.isSecondLevelCacheCheckingEnabled() ) {
 				LoadEvent loadEvent = new LoadEvent(
 						id,
-						entityDescriptor.getMappedClass().getName(),
+						getLoadable().getJavaType().getJavaTypeClass().getName(),
 						lockOptions,
 						session,
-						getReadOnlyFromLoadQueryInfluencers(session)
+						LoaderHelper.getReadOnlyFromLoadQueryInfluencers(session)
 				);
 
 				Object managedEntity = null;
@@ -163,7 +142,7 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 					// look for it in the SessionFactory
 					managedEntity = CacheEntityLoaderHelper.INSTANCE.loadFromSecondLevelCache(
 							loadEvent,
-							entityDescriptor,
+							getLoadable().getEntityPersister(),
 							entityKey
 					);
 				}
@@ -184,8 +163,7 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 				idsInBatch.clear();
 			}
 
-			// Save the EntityKey instance for use later!
+			// Save the EntityKey instance for use later
-			// todo (6.0) : see below wrt why `elementPositionsLoadedByBatch` probably isn't needed
 			result.add( i, entityKey );
 			elementPositionsLoadedByBatch.add( i );
 		}
@@ -196,8 +174,7 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 			loadEntitiesById( idsInBatch, lockOptions, session );
 		}
 
-		// todo (6.0) : can't we just walk all elements of the results looking for EntityKey and replacing here?
+		// for each result where we set the EntityKey earlier, replace them
-		//		can't imagine
 		final PersistenceContext persistenceContext = session.getPersistenceContextInternal();
 		for ( Integer position : elementPositionsLoadedByBatch ) {
 			// the element value at this position in the result List should be
@@ -232,7 +209,7 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 		}
 
 		if ( log.isTraceEnabled() ) {
-			log.tracef( "#loadEntitiesById(`%s`, `%s`, ..)", entityDescriptor.getEntityName(), numberOfIdsInBatch );
+			log.tracef( "#loadEntitiesById(`%s`, `%s`, ..)", getLoadable().getEntityName(), numberOfIdsInBatch );
 		}
 
 		final List<JdbcParameter> jdbcParameters = new ArrayList<>( numberOfIdsInBatch * idJdbcTypeCount);
@@ -247,10 +224,10 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 				session.getLoadQueryInfluencers(),
 				lockOptions,
 				jdbcParameters::add,
-				sessionFactory
+				getSessionFactory()
 		);
 
-		final JdbcServices jdbcServices = sessionFactory.getJdbcServices();
+		final JdbcServices jdbcServices = getSessionFactory().getJdbcServices();
 		final JdbcEnvironment jdbcEnvironment = jdbcServices.getJdbcEnvironment();
 		final SqlAstTranslatorFactory sqlAstTranslatorFactory = jdbcEnvironment.getSqlAstTranslatorFactory();
 
@@ -263,7 +240,7 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 			offset += jdbcParameterBindings.registerParametersForEachJdbcValue(
 					id,
 					offset,
-					entityDescriptor.getIdentifierMapping(),
+					getLoadable().getIdentifierMapping(),
 					jdbcParameters,
 					session
 			);
@@ -271,11 +248,11 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 
 		// we should have used all the JdbcParameter references (created bindings for all)
 		assert offset == jdbcParameters.size();
-		final JdbcOperationQuerySelect jdbcSelect = sqlAstTranslatorFactory.buildSelectTranslator( sessionFactory, sqlAst )
+		final JdbcOperationQuerySelect jdbcSelect = sqlAstTranslatorFactory.buildSelectTranslator( getSessionFactory(), sqlAst )
 				.translate( jdbcParameterBindings, QueryOptions.NONE );
 
 		final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler;
-		if ( entityDescriptor.hasSubselectLoadableCollections() ) {
+		if ( getLoadable().getEntityPersister().hasSubselectLoadableCollections() ) {
 			subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
 					session.getPersistenceContext().getBatchFetchQueue(),
 					sqlAst,
@@ -297,19 +274,21 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 	}
 
 	private List<T> performSingleMultiLoad(Object id, LockOptions lockOptions, SharedSessionContractImplementor session) {
-		T loaded = (T) entityDescriptor.load( id, null, lockOptions, session );
+		//noinspection unchecked
+		T loaded = (T) getLoadable().getEntityPersister().load( id, null, lockOptions, session );
 		return Collections.singletonList( loaded );
 	}
 
-	private List<T> performUnorderedMultiLoad(
+	@Override
+	protected List<T> performUnorderedMultiLoad(
 			Object[] ids,
-			EventSource session,
+			MultiIdLoadOptions loadOptions,
-			MultiIdLoadOptions loadOptions) {
+			EventSource session) {
 		assert !loadOptions.isOrderReturnEnabled();
 		assert ids != null;
 
 		if ( log.isTraceEnabled() ) {
-			log.tracef( "#performUnorderedMultiLoad(`%s`, ..)", entityDescriptor.getEntityName() );
+			log.tracef( "#performUnorderedMultiLoad(`%s`, ..)", getLoadable().getEntityName() );
 		}
 
 		final List<T> result = CollectionHelper.arrayList( ids.length );
@@ -327,23 +306,23 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 			boolean foundAnyManagedEntities = false;
 			final List<Object> nonManagedIds = new ArrayList<>();
 
-			final boolean coerce = !sessionFactory.getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
+			final boolean coerce = !getSessionFactory().getJpaMetamodel().getJpaCompliance().isLoadByIdComplianceEnabled();
 			for ( int i = 0; i < ids.length; i++ ) {
 				final Object id;
 				if ( coerce ) {
-					id = entityDescriptor.getIdentifierMapping().getJavaType().coerce( ids[i], session );
+					id = getLoadable().getIdentifierMapping().getJavaType().coerce( ids[i], session );
 				}
 				else {
 					id = ids[i];
 				}
-				final EntityKey entityKey = new EntityKey( id, entityDescriptor );
+				final EntityKey entityKey = new EntityKey( id, getLoadable().getEntityPersister() );
 
 				LoadEvent loadEvent = new LoadEvent(
 						id,
-						entityDescriptor.getMappedClass().getName(),
+						getLoadable().getJavaType().getJavaTypeClass().getName(),
 						lockOptions,
 						session,
-						getReadOnlyFromLoadQueryInfluencers( session )
+						LoaderHelper.getReadOnlyFromLoadQueryInfluencers( session )
 				);
 
 				Object managedEntity = null;
@@ -370,7 +349,7 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 				if ( managedEntity == null && loadOptions.isSecondLevelCacheCheckingEnabled() ) {
 					managedEntity = CacheEntityLoaderHelper.INSTANCE.loadFromSecondLevelCache(
 							loadEvent,
-							entityDescriptor,
+							getLoadable().getEntityPersister(),
 							entityKey
 					);
 				}
@@ -409,10 +388,10 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 			maxBatchSize = loadOptions.getBatchSize();
 		}
 		else {
-			maxBatchSize = session.getJdbcServices().getJdbcEnvironment().getDialect().getDefaultBatchLoadSizingStrategy().determineOptimalBatchLoadSize(
+			maxBatchSize = session.getJdbcServices().getJdbcEnvironment().getDialect().getBatchLoadSizingStrategy().determineOptimalBatchLoadSize(
-					entityDescriptor.getIdentifierType().getColumnSpan( session.getFactory() ),
+					getIdentifierMapping().getJdbcTypeCount(),
 					numberOfIdsLeft,
-					sessionFactory.getSessionFactoryOptions().inClauseParameterPaddingEnabled()
+					getSessionFactory().getSessionFactoryOptions().inClauseParameterPaddingEnabled()
 			);
 		}
 
@@ -434,13 +413,4 @@ public class MultiIdLoaderStandard<T> implements MultiIdEntityLoader<T> {
 		return result;
 	}
 
-	private Boolean getReadOnlyFromLoadQueryInfluencers(SharedSessionContractImplementor session) {
-		Boolean readOnly = null;
-		final LoadQueryInfluencers loadQueryInfluencers = session.getLoadQueryInfluencers();
-		if ( loadQueryInfluencers != null ) {
-			readOnly = loadQueryInfluencers.getReadOnly();
-		}
-		return readOnly;
-	}
-
 }

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiKeyLoadChunker.java

@@ -0,0 +1,162 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.util.List;
+
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.metamodel.mapping.Bindable;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
+import org.hibernate.sql.exec.spi.ExecutionContext;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
+import org.hibernate.sql.results.spi.ListResultsConsumer;
+
+/**
+ * When the number of ids to initialize exceeds a certain threshold, IN-predicate based
+ * {@linkplain org.hibernate.loader.ast.spi.MultiKeyLoader multi-key loaders} will break
+ * the initialization into "chunks".
+ *
+ * @author Steve Ebersole
+ */
+public class MultiKeyLoadChunker<K> {
+	@FunctionalInterface
+	interface SqlExecutionContextCreator {
+		ExecutionContext createContext(
+				JdbcParameterBindings parameterBindings,
+				SharedSessionContractImplementor session);
+	}
+
+	@FunctionalInterface
+	interface KeyCollector<K> {
+		void collect(K key, int relativePosition, int absolutePosition);
+	}
+
+	@FunctionalInterface
+	interface ChunkStartListener {
+		void chunkStartNotification(int startIndex);
+	}
+
+	@FunctionalInterface
+	interface ChunkBoundaryListener {
+		void chunkBoundaryNotification(int startIndex, int nonNullElementCount);
+	}
+
+	private final int chunkSize;
+	private final int keyColumnCount;
+	private final Bindable bindable;
+
+	private final List<JdbcParameter> jdbcParameters;
+	private final SelectStatement sqlAst;
+	private final JdbcOperationQuerySelect jdbcSelect;
+
+	public MultiKeyLoadChunker(
+			int chunkSize,
+			int keyColumnCount,
+			Bindable bindable,
+			List<JdbcParameter> jdbcParameters,
+			SelectStatement sqlAst,
+			JdbcOperationQuerySelect jdbcSelect) {
+		this.chunkSize = chunkSize;
+		this.keyColumnCount = keyColumnCount;
+		this.bindable = bindable;
+		this.jdbcParameters = jdbcParameters;
+		this.sqlAst = sqlAst;
+		this.jdbcSelect = jdbcSelect;
+	}
+
+	/**
+	 * Process the chunks
+	 *
+	 * @param keys The group of keys to be initialized
+	 * @param nonNullElementCount The number of non-null values in {@code keys}, which will be
+	 * 		less-than-or-equal-to the number of {@code keys}
+	 * @param startListener Notifications that processing a chunk has starting
+	 * @param keyCollector Called for each key as it is processed
+	 * @param boundaryListener Notifications that processing a chunk has completed
+	 */
+	public void processChunks(
+			K[] keys,
+			int nonNullElementCount,
+			SqlExecutionContextCreator sqlExecutionContextCreator,
+			KeyCollector<K> keyCollector,
+			ChunkStartListener startListener,
+			ChunkBoundaryListener boundaryListener,
+			SharedSessionContractImplementor session) {
+		int numberOfKeysLeft = nonNullElementCount;
+		int start = 0;
+		while ( numberOfKeysLeft > 0 ) {
+			processChunk( keys, start, sqlExecutionContextCreator, keyCollector, startListener, boundaryListener, session );
+
+			start += chunkSize;
+			numberOfKeysLeft -= chunkSize;
+		}
+	}
+
+	private void processChunk(
+			K[] keys,
+			int startIndex,
+			SqlExecutionContextCreator sqlExecutionContextCreator,
+			KeyCollector<K> keyCollector,
+			ChunkStartListener startListener,
+			ChunkBoundaryListener boundaryListener,
+			SharedSessionContractImplementor session) {
+		startListener.chunkStartNotification( startIndex );
+
+		final int parameterCount = chunkSize * keyColumnCount;
+		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl( parameterCount );
+
+		int nonNullCounter = 0;
+		int bindCount = 0;
+		for ( int i = 0; i < chunkSize; i++ ) {
+			// the position within `K[] keys`
+			final int keyPosition = i + startIndex;
+
+			final K value;
+			if ( keyPosition >= keys.length ) {
+				value = null;
+			}
+			else {
+				value = keys[keyPosition];
+			}
+
+			keyCollector.collect( value, i, keyPosition );
+
+			if ( value != null ) {
+				nonNullCounter++;
+			}
+
+			bindCount += jdbcParameterBindings.registerParametersForEachJdbcValue(
+					value,
+					bindCount,
+					bindable,
+					jdbcParameters,
+					session
+			);
+		}
+		assert bindCount == jdbcParameters.size();
+
+		if ( nonNullCounter == 0 ) {
+			// there are no non-null keys in the chunk
+			return;
+		}
+
+		session.getFactory().getJdbcServices().getJdbcSelectExecutor().list(
+				jdbcSelect,
+				jdbcParameterBindings,
+				sqlExecutionContextCreator.createContext( jdbcParameterBindings, session ),
+				RowTransformerStandardImpl.instance(),
+				ListResultsConsumer.UniqueSemantic.FILTER
+		);
+
+		boundaryListener.chunkBoundaryNotification( startIndex, nonNullCounter );
+	}
+
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiKeyLoadHelper.java

@@ -0,0 +1,59 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import org.hibernate.dialect.Dialect;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.metamodel.mapping.JdbcMapping;
+import org.hibernate.type.BasicType;
+import org.hibernate.type.SqlTypes;
+import org.hibernate.type.descriptor.java.BasicPluralJavaType;
+import org.hibernate.type.descriptor.java.JavaType;
+import org.hibernate.type.descriptor.java.spi.JavaTypeRegistry;
+import org.hibernate.type.spi.TypeConfiguration;
+
+/**
+ * @author Steve Ebersole
+ */
+public class MultiKeyLoadHelper {
+	private MultiKeyLoadHelper() {
+	}
+
+	public static boolean supportsSqlArrayType(Dialect dialect) {
+		return dialect.supportsStandardArrays()
+				&& dialect.getPreferredSqlTypeCodeForArray() == SqlTypes.ARRAY;
+	}
+
+	public static JdbcMapping resolveArrayJdbcMapping(
+			BasicType<?> arrayBasicType,
+			JdbcMapping keyMapping,
+			Class<?> arrayClass,
+			SessionFactoryImplementor sessionFactory) {
+		if ( arrayBasicType != null ) {
+			return arrayBasicType;
+		}
+
+		final TypeConfiguration typeConfiguration = sessionFactory.getTypeConfiguration();
+		final JavaTypeRegistry javaTypeRegistry = typeConfiguration.getJavaTypeRegistry();
+
+		final JavaType<Object> rawArrayJavaType = javaTypeRegistry.resolveDescriptor( arrayClass );
+		if ( !(rawArrayJavaType instanceof BasicPluralJavaType ) ) {
+			throw new IllegalArgumentException( "Expecting BasicPluralJavaType for array class `" + arrayClass.getName() + "`, but got `" + rawArrayJavaType + "`" );
+		}
+
+		final BasicPluralJavaType<?> arrayJavaType = (BasicPluralJavaType<?>) rawArrayJavaType;
+		//noinspection unchecked,rawtypes
+		return arrayJavaType.resolveType(
+				typeConfiguration,
+				sessionFactory.getJdbcServices().getDialect(),
+				// potentially problematic - custom id type
+				(BasicType) keyMapping,
+				null,
+				typeConfiguration.getCurrentBaseSqlTypeIndicators()
+		);
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiKeyLoadLogging.java

@@ -0,0 +1,34 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.loader.ast.internal;
+
+import org.hibernate.internal.log.SubSystemLogging;
+
+import org.jboss.logging.Logger;
+
+/**
+ * Logging related to loading a {@linkplain org.hibernate.loader.ast.spi.Loadable loadable}
+ * by multiple "keys".  The key can be primary, foreign or natural.
+ *
+ * @see org.hibernate.annotations.BatchSize
+ * @see org.hibernate.Session#byMultipleIds
+ * @see org.hibernate.Session#byMultipleNaturalId
+ *
+ * @author Steve Ebersole
+ */
+@SubSystemLogging(
+		name = MultiKeyLoadLogging.LOGGER_NAME,
+		description = "Logging related to multi-key loading of entity and collection references"
+)
+public interface MultiKeyLoadLogging {
+	String LOGGER_NAME = SubSystemLogging.BASE + ".loader.multi";
+
+	Logger MULTI_KEY_LOAD_LOGGER = Logger.getLogger( LOGGER_NAME );
+
+	boolean MULTI_KEY_LOAD_TRACE_ENABLED = MULTI_KEY_LOAD_LOGGER.isTraceEnabled();
+	boolean MULTI_KEY_LOAD_DEBUG_ENABLED = MULTI_KEY_LOAD_LOGGER.isDebugEnabled();
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiNaturalIdLoaderArrayParam.java

@@ -0,0 +1,120 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.util.Collections;
+import java.util.List;
+
+import org.hibernate.LockMode;
+import org.hibernate.LockOptions;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.loader.ast.spi.MultiNaturalIdLoadOptions;
+import org.hibernate.loader.ast.spi.MultiNaturalIdLoader;
+import org.hibernate.loader.ast.spi.SqlArrayMultiKeyLoader;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.metamodel.mapping.JdbcMapping;
+import org.hibernate.metamodel.mapping.internal.BasicAttributeMapping;
+import org.hibernate.metamodel.mapping.internal.SimpleNaturalIdMapping;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+import org.hibernate.sql.ast.tree.select.SelectStatement;
+import org.hibernate.sql.exec.internal.JdbcParameterImpl;
+import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
+import org.hibernate.sql.exec.spi.JdbcParameterBindings;
+import org.hibernate.type.BasicType;
+import org.hibernate.type.BasicTypeRegistry;
+
+/**
+ * Standard MultiNaturalIdLoader implementation
+ */
+public class MultiNaturalIdLoaderArrayParam<E> implements MultiNaturalIdLoader<E>, SqlArrayMultiKeyLoader {
+	private final EntityMappingType entityDescriptor;
+	private final Class<?> keyArrayClass;
+
+	public MultiNaturalIdLoaderArrayParam(EntityMappingType entityDescriptor) {
+		assert entityDescriptor.getNaturalIdMapping() instanceof SimpleNaturalIdMapping;
+
+		this.entityDescriptor = entityDescriptor;
+
+		final Class<?> keyClass = entityDescriptor.getNaturalIdMapping().getJavaType().getJavaTypeClass();
+		this.keyArrayClass = LoaderHelper.createTypedArray( keyClass, 0 ).getClass();
+	}
+
+	@Override
+	public EntityMappingType getLoadable() {
+		return entityDescriptor;
+	}
+
+	protected SimpleNaturalIdMapping getNaturalIdMapping()  {
+		return (SimpleNaturalIdMapping) entityDescriptor.getNaturalIdMapping();
+	}
+
+	protected BasicAttributeMapping getNaturalIdAttribute()  {
+		return (BasicAttributeMapping) getNaturalIdMapping().asAttributeMapping();
+	}
+
+	@Override
+	public <K> List<E> multiLoad(K[] naturalIds, MultiNaturalIdLoadOptions loadOptions, SharedSessionContractImplementor session) {
+		if ( naturalIds == null ) {
+			throw new IllegalArgumentException( "`naturalIds` is null" );
+		}
+
+		if ( naturalIds.length == 0 ) {
+			return Collections.emptyList();
+		}
+
+		if ( MultiKeyLoadLogging.MULTI_KEY_LOAD_TRACE_ENABLED ) {
+			MultiKeyLoadLogging.MULTI_KEY_LOAD_LOGGER.tracef( "MultiNaturalIdLoaderArrayParam#multiLoadStarting - `%s`", entityDescriptor.getEntityName() );
+		}
+
+		final SessionFactoryImplementor sessionFactory = session.getFactory();
+		naturalIds = LoaderHelper.normalizeKeys( naturalIds, getNaturalIdAttribute(), session, sessionFactory );
+
+		final LockOptions lockOptions = (loadOptions.getLockOptions() == null)
+				? new LockOptions( LockMode.NONE )
+				: loadOptions.getLockOptions();
+
+		final BasicTypeRegistry basicTypeRegistry = sessionFactory.getTypeConfiguration().getBasicTypeRegistry();
+		final BasicType<?> arrayBasicType = basicTypeRegistry.getRegisteredType( keyArrayClass );
+		final JdbcMapping arrayJdbcMapping = MultiKeyLoadHelper.resolveArrayJdbcMapping(
+				arrayBasicType,
+				getNaturalIdMapping().getSingleJdbcMapping(),
+				keyArrayClass,
+				sessionFactory
+		);
+		final JdbcParameter jdbcParameter = new JdbcParameterImpl( arrayJdbcMapping );
+
+		final SelectStatement sqlAst = LoaderSelectBuilder.createSelectBySingleArrayParameter(
+				getLoadable(),
+				getNaturalIdAttribute(),
+				session.getLoadQueryInfluencers(),
+				lockOptions,
+				jdbcParameter,
+				sessionFactory
+		);
+		final JdbcOperationQuerySelect jdbcSelectOperation = sessionFactory.getJdbcServices()
+				.getJdbcEnvironment()
+				.getSqlAstTranslatorFactory()
+				.buildSelectTranslator( sessionFactory, sqlAst )
+				.translate( JdbcParameterBindings.NO_BINDINGS, QueryOptions.NONE );
+
+		return LoaderHelper.loadByArrayParameter(
+				naturalIds,
+				sqlAst,
+				jdbcSelectOperation,
+				jdbcParameter,
+				arrayJdbcMapping,
+				null,
+				null,
+				lockOptions,
+				session.isDefaultReadOnly(),
+				session
+		);
+	}
+
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/MultiNaturalIdLoaderInPredicate.java

@@ -15,21 +15,17 @@ import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.loader.ast.spi.MultiNaturalIdLoadOptions;
 import org.hibernate.loader.ast.spi.MultiNaturalIdLoader;
+import org.hibernate.loader.ast.spi.SqlInPredicateMultiKeyLoader;
 import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.sql.results.LoadingLogger;
 
 /**
- * Standard MultiNaturalIdLoader implementation
+ * MultiNaturalIdLoader implementation using SQL IN predicate to specify the ids
  */
-public class MultiNaturalIdLoaderStandard<E> implements MultiNaturalIdLoader<E> {
+public class MultiNaturalIdLoaderInPredicate<E> implements MultiNaturalIdLoader<E>, SqlInPredicateMultiKeyLoader {
-
-	// todo (6.0) : much of the execution logic here is borrowed from `org.hibernate.loader.ast.internal.MultiIdEntityLoaderStandardImpl`
-	// 	- consider ways to consolidate/share logic
-	//		- actually, org.hibernate.loader.ast.internal.MultiNaturalIdLoadingBatcher is pretty close
-
 	private final EntityMappingType entityDescriptor;
 
-	public MultiNaturalIdLoaderStandard(EntityMappingType entityDescriptor) {
+	public MultiNaturalIdLoaderInPredicate(EntityMappingType entityDescriptor) {
 		this.entityDescriptor = entityDescriptor;
 	}
 
@@ -54,7 +50,7 @@ public class MultiNaturalIdLoaderStandard<E> implements MultiNaturalIdLoader<E>
 			maxBatchSize = options.getBatchSize();
 		}
 		else {
-			maxBatchSize = session.getJdbcServices().getJdbcEnvironment().getDialect().getDefaultBatchLoadSizingStrategy().determineOptimalBatchLoadSize(
+			maxBatchSize = session.getJdbcServices().getJdbcEnvironment().getDialect().getMultiKeyLoadSizingStrategy().determineOptimalBatchLoadSize(
 					entityDescriptor.getNaturalIdMapping().getJdbcTypeCount(),
 					naturalIds.length,
 					sessionFactory.getSessionFactoryOptions().inClauseParameterPaddingEnabled()

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/SingleIdEntityLoaderDynamicBatch.java

@@ -1,243 +0,0 @@
-/*
- * Hibernate, Relational Persistence for Idiomatic Java
- *
- * License: GNU Lesser General Public License (LGPL), version 2.1 or later
- * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
- */
-package org.hibernate.loader.ast.internal;
-
-import java.util.ArrayList;
-import java.util.List;
-
-import org.hibernate.LockOptions;
-import org.hibernate.engine.internal.BatchFetchQueueHelper;
-import org.hibernate.engine.jdbc.env.spi.JdbcEnvironment;
-import org.hibernate.engine.jdbc.spi.JdbcServices;
-import org.hibernate.engine.spi.EntityKey;
-import org.hibernate.engine.spi.SessionFactoryImplementor;
-import org.hibernate.engine.spi.SharedSessionContractImplementor;
-import org.hibernate.engine.spi.SubselectFetch;
-import org.hibernate.internal.util.collections.ArrayHelper;
-import org.hibernate.metamodel.mapping.EntityMappingType;
-import org.hibernate.query.spi.QueryOptions;
-import org.hibernate.query.spi.QueryOptionsAdapter;
-import org.hibernate.sql.ast.SqlAstTranslatorFactory;
-import org.hibernate.sql.ast.tree.expression.JdbcParameter;
-import org.hibernate.sql.ast.tree.select.SelectStatement;
-import org.hibernate.sql.exec.internal.BaseExecutionContext;
-import org.hibernate.sql.exec.internal.JdbcParameterBindingsImpl;
-import org.hibernate.sql.exec.spi.ExecutionContext;
-import org.hibernate.sql.exec.spi.JdbcOperationQuerySelect;
-import org.hibernate.sql.exec.spi.JdbcParameterBindings;
-import org.hibernate.sql.results.graph.entity.LoadingEntityEntry;
-import org.hibernate.sql.results.internal.RowTransformerStandardImpl;
-import org.hibernate.sql.results.spi.ListResultsConsumer;
-
-import org.jboss.logging.Logger;
-
-/**
- * @author Steve Ebersole
- */
-public class SingleIdEntityLoaderDynamicBatch<T> extends SingleIdEntityLoaderSupport<T> {
-	private static final Logger log = Logger.getLogger( SingleIdEntityLoaderDynamicBatch.class );
-
-	private final int maxBatchSize;
-
-	private SingleIdEntityLoaderStandardImpl<T> singleIdLoader;
-
-	public SingleIdEntityLoaderDynamicBatch(
-			EntityMappingType entityDescriptor,
-			int maxBatchSize,
-			SessionFactoryImplementor sessionFactory) {
-		super( entityDescriptor, sessionFactory );
-		this.maxBatchSize = maxBatchSize;
-	}
-
-	@Override
-	public T load(Object pkValue, LockOptions lockOptions, Boolean readOnly, SharedSessionContractImplementor session) {
-		return load( pkValue, null, lockOptions, readOnly, session );
-	}
-
-	@Override
-	public T load(
-			Object pkValue,
-			Object entityInstance,
-			LockOptions lockOptions,
-			Boolean readOnly,
-			SharedSessionContractImplementor session) {
-		final Object[] batchIds = session.getPersistenceContextInternal()
-				.getBatchFetchQueue()
-				.getBatchLoadableEntityIds( getLoadable(), pkValue, maxBatchSize );
-
-		final int numberOfIds = ArrayHelper.countNonNull( batchIds );
-		if ( numberOfIds <= 1 ) {
-			initializeSingleIdLoaderIfNeeded( session );
-
-			final T result = singleIdLoader.load( pkValue, entityInstance, lockOptions, readOnly, session );
-			if ( result == null ) {
-				// There was no entity with the specified ID. Make sure the EntityKey does not remain
-				// in the batch to avoid including it in future batches that get executed.
-				BatchFetchQueueHelper.removeBatchLoadableEntityKey( pkValue, getLoadable(), session );
-			}
-
-			return result;
-		}
-
-		final Object[] idsToLoad = new Object[numberOfIds];
-		System.arraycopy( batchIds, 0, idsToLoad, 0, numberOfIds );
-
-		if ( log.isDebugEnabled() ) {
-			log.debugf( "Batch loading entity [%s] : %s", getLoadable().getEntityName(), idsToLoad );
-		}
-
-		final List<JdbcParameter> jdbcParameters = new ArrayList<>();
-
-		final SelectStatement sqlAst = LoaderSelectBuilder.createSelect(
-				getLoadable(),
-				// null here means to select everything
-				null,
-				getLoadable().getIdentifierMapping(),
-				null,
-				numberOfIds,
-				session.getLoadQueryInfluencers(),
-				lockOptions,
-				jdbcParameters::add,
-				session.getFactory()
-		);
-
-		final SessionFactoryImplementor sessionFactory = session.getFactory();
-		final JdbcServices jdbcServices = sessionFactory.getJdbcServices();
-		final JdbcEnvironment jdbcEnvironment = jdbcServices.getJdbcEnvironment();
-		final SqlAstTranslatorFactory sqlAstTranslatorFactory = jdbcEnvironment.getSqlAstTranslatorFactory();
-
-		final JdbcParameterBindings jdbcParameterBindings = new JdbcParameterBindingsImpl(
-				getLoadable().getIdentifierMapping().getJdbcTypeCount()
-		);
-
-		int offset = 0;
-		for ( int i = 0; i < numberOfIds; i++ ) {
-			offset += jdbcParameterBindings.registerParametersForEachJdbcValue(
-					idsToLoad[i],
-					offset,
-					getLoadable().getIdentifierMapping(),
-					jdbcParameters,
-					session
-			);
-		}
-		assert offset == jdbcParameters.size();
-
-		final JdbcOperationQuerySelect jdbcSelect = sqlAstTranslatorFactory
-				.buildSelectTranslator( sessionFactory, sqlAst )
-				.translate( jdbcParameterBindings, QueryOptions.NONE );
-
-		final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler = SubselectFetch.createRegistrationHandler(
-				session.getPersistenceContext().getBatchFetchQueue(),
-				sqlAst,
-				jdbcParameters,
-				jdbcParameterBindings
-		);
-
-		session.getJdbcServices().getJdbcSelectExecutor().list(
-				jdbcSelect,
-				jdbcParameterBindings,
-				getExecutionContext(
-						pkValue,
-						entityInstance,
-						readOnly,
-						lockOptions,
-						session,
-						subSelectFetchableKeysHandler
-				),
-				RowTransformerStandardImpl.instance(),
-				ListResultsConsumer.UniqueSemantic.FILTER
-		);
-
-		//noinspection ForLoopReplaceableByForEach
-		for ( int i = 0; i < idsToLoad.length; i++ ) {
-			final Object id = idsToLoad[i];
-			// found or not, remove the key from the batch-fetch queye
-			BatchFetchQueueHelper.removeBatchLoadableEntityKey( id, getLoadable(), session );
-		}
-
-		final EntityKey entityKey = session.generateEntityKey( pkValue, getLoadable().getEntityPersister() );
-		//noinspection unchecked
-		return (T) session.getPersistenceContext().getEntity( entityKey );
-	}
-
-	private ExecutionContext getExecutionContext(
-			Object entityId,
-			Object entityInstance,
-			Boolean readOnly,
-			LockOptions lockOptions,
-			SharedSessionContractImplementor session,
-			SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler) {
-		return new SingleIdExecutionContext( session,
-											entityInstance,
-											entityId,
-											readOnly,
-											lockOptions,
-											subSelectFetchableKeysHandler
-		);
-	}
-
-	private void initializeSingleIdLoaderIfNeeded(SharedSessionContractImplementor session) {
-		if ( singleIdLoader == null ) {
-			singleIdLoader = new SingleIdEntityLoaderStandardImpl<>( getLoadable(), session.getFactory() );
-			singleIdLoader.prepare();
-		}
-	}
-
-	private static class SingleIdExecutionContext extends BaseExecutionContext {
-		private final Object entityInstance;
-		private final Object entityId;
-		private final Boolean readOnly;
-		private final LockOptions lockOptions;
-		private final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler;
-
-		public SingleIdExecutionContext(
-				SharedSessionContractImplementor session,
-				Object entityInstance,
-				Object entityId,
-				Boolean readOnly,
-				LockOptions lockOptions,
-				SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler) {
-			super( session );
-			this.entityInstance = entityInstance;
-			this.entityId = entityId;
-			this.readOnly = readOnly;
-			this.lockOptions = lockOptions;
-			this.subSelectFetchableKeysHandler = subSelectFetchableKeysHandler;
-		}
-
-		@Override
-		public Object getEntityInstance() {
-			return entityInstance;
-		}
-
-		@Override
-		public Object getEntityId() {
-			return entityId;
-		}
-
-		@Override
-		public QueryOptions getQueryOptions() {
-			return new QueryOptionsAdapter() {
-				@Override
-				public Boolean isReadOnly() {
-					return readOnly;
-				}
-
-				@Override
-				public LockOptions getLockOptions() {
-					return lockOptions;
-				}
-			};
-		}
-
-		@Override
-		public void registerLoadingEntityEntry(EntityKey entityKey, LoadingEntityEntry entry) {
-			subSelectFetchableKeysHandler.addKey( entityKey, entry );
-		}
-
-	}
-}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/SingleIdExecutionContext.java

@@ -0,0 +1,73 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import org.hibernate.LockOptions;
+import org.hibernate.engine.spi.EntityKey;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.engine.spi.SubselectFetch;
+import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.query.spi.QueryOptionsAdapter;
+import org.hibernate.sql.exec.internal.BaseExecutionContext;
+import org.hibernate.sql.results.graph.entity.LoadingEntityEntry;
+
+/**
+ * @author Steve Ebersole
+ */
+class SingleIdExecutionContext extends BaseExecutionContext {
+	private final Object entityInstance;
+	private final Object entityId;
+	private final Boolean readOnly;
+	private final LockOptions lockOptions;
+	private final SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler;
+
+	public SingleIdExecutionContext(
+			Object entityId,
+			Object entityInstance,
+			Boolean readOnly,
+			LockOptions lockOptions,
+			SubselectFetch.RegistrationHandler subSelectFetchableKeysHandler,
+			SharedSessionContractImplementor session) {
+		super( session );
+		this.entityInstance = entityInstance;
+		this.entityId = entityId;
+		this.readOnly = readOnly;
+		this.lockOptions = lockOptions;
+		this.subSelectFetchableKeysHandler = subSelectFetchableKeysHandler;
+	}
+
+	@Override
+	public Object getEntityInstance() {
+		return entityInstance;
+	}
+
+	@Override
+	public Object getEntityId() {
+		return entityId;
+	}
+
+	@Override
+	public QueryOptions getQueryOptions() {
+		return new QueryOptionsAdapter() {
+			@Override
+			public Boolean isReadOnly() {
+				return readOnly;
+			}
+
+			@Override
+			public LockOptions getLockOptions() {
+				return lockOptions;
+			}
+		};
+	}
+
+	@Override
+	public void registerLoadingEntityEntry(EntityKey entityKey, LoadingEntityEntry entry) {
+		subSelectFetchableKeysHandler.addKey( entityKey, entry );
+	}
+
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/SingleIdLoadPlan.java

@@ -14,6 +14,7 @@ import org.hibernate.engine.jdbc.spi.JdbcServices;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.loader.ast.spi.Loadable;
+import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.metamodel.mapping.ModelPart;
 import org.hibernate.query.internal.SimpleQueryOptions;
 import org.hibernate.query.spi.QueryOptions;
@@ -41,20 +42,20 @@ import org.hibernate.sql.results.spi.RowTransformer;
  * @author Steve Ebersole
  */
 public class SingleIdLoadPlan<T> implements SingleEntityLoadPlan {
-	private final org.hibernate.persister.entity.Loadable persister;
+	private final EntityMappingType entityMappingType;
 	private final ModelPart restrictivePart;
 	private final LockOptions lockOptions;
 	private final JdbcOperationQuerySelect jdbcSelect;
 	private final List<JdbcParameter> jdbcParameters;
 
 	public SingleIdLoadPlan(
-			org.hibernate.persister.entity.Loadable persister,
+			EntityMappingType entityMappingType,
 			ModelPart restrictivePart,
 			SelectStatement sqlAst,
 			List<JdbcParameter> jdbcParameters,
 			LockOptions lockOptions,
 			SessionFactoryImplementor sessionFactory) {
-		this.persister = persister;
+		this.entityMappingType = entityMappingType;
 		this.restrictivePart = restrictivePart;
 		this.lockOptions = lockOptions.makeCopy();
 		this.jdbcParameters = jdbcParameters;
@@ -83,7 +84,7 @@ public class SingleIdLoadPlan<T> implements SingleEntityLoadPlan {
 
 	@Override
 	public Loadable getLoadable() {
-		return persister;
+		return entityMappingType;
 	}
 
 	@Override
@@ -154,8 +155,8 @@ public class SingleIdLoadPlan<T> implements SingleEntityLoadPlan {
 		}
 
 		final T entity = list.get( 0 );
-		if ( persister != null ) {
+		if ( entityMappingType != null ) {
-			callback.invokeAfterLoadActions( session, entity, persister );
+			callback.invokeAfterLoadActions( entity, entityMappingType, session );
 		}
 		return entity;
 	}

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/SingleUniqueKeyEntityLoaderStandard.java

@@ -73,7 +73,6 @@ public class SingleUniqueKeyEntityLoaderStandard<T> implements SingleUniqueKeyEn
 				Collections.emptyList(),
 				uniqueKeyAttribute,
 				null,
-				1,
 				LoadQueryInfluencers.NONE,
 				LockOptions.NONE,
 				jdbcParameters::add,
@@ -129,7 +128,6 @@ public class SingleUniqueKeyEntityLoaderStandard<T> implements SingleUniqueKeyEn
 				Collections.singletonList( entityDescriptor.getIdentifierMapping() ),
 				uniqueKeyAttribute,
 				null,
-				1,
 				LoadQueryInfluencers.NONE,
 				LockOptions.NONE,
 				jdbcParameters::add,

hibernate-core/src/main/java/org/hibernate/loader/ast/internal/StandardBatchLoaderFactory.java

@@ -0,0 +1,74 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.internal;
+
+import java.util.Map;
+
+import org.hibernate.dialect.Dialect;
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.loader.ast.spi.BatchLoaderFactory;
+import org.hibernate.loader.ast.spi.CollectionBatchLoader;
+import org.hibernate.loader.ast.spi.EntityBatchLoader;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
+import org.hibernate.service.spi.ServiceRegistryImplementor;
+import org.hibernate.type.BasicType;
+import org.hibernate.type.SqlTypes;
+import org.hibernate.type.Type;
+
+/**
+ * Standard {@link BatchLoaderFactory} implementation
+ *
+ * @author Steve Ebersole
+ */
+public class StandardBatchLoaderFactory implements BatchLoaderFactory {
+	@SuppressWarnings("unused")
+	public StandardBatchLoaderFactory(Map<String, Object> configurationValues, ServiceRegistryImplementor registry) {
+	}
+
+	@Override
+	public <T> EntityBatchLoader<T> createEntityBatchLoader(
+			int domainBatchSize, EntityMappingType entityDescriptor,
+			SessionFactoryImplementor factory) {
+		final Dialect dialect = factory.getJdbcServices().getDialect();
+
+		// NOTE : don't use the EntityIdentifierMapping here because it will not be known until later
+		final Type identifierType = entityDescriptor.getEntityPersister().getIdentifierType();
+		final int idColumnCount = identifierType.getColumnSpan( factory );
+
+		if ( idColumnCount == 1
+				&& MultiKeyLoadHelper.supportsSqlArrayType( dialect )
+				&& identifierType instanceof BasicType ) {
+			// we can use a single ARRAY parameter to send all the ids
+			return new EntityBatchLoaderArrayParam<>( domainBatchSize, entityDescriptor, factory );
+		}
+
+		final int optimalBatchSize = dialect
+				.getBatchLoadSizingStrategy()
+				.determineOptimalBatchLoadSize( idColumnCount, domainBatchSize, false );
+		return new EntityBatchLoaderInPredicate<>( domainBatchSize, optimalBatchSize, entityDescriptor, factory );
+	}
+
+	@Override
+	public CollectionBatchLoader createCollectionBatchLoader(
+			int domainBatchSize,
+			LoadQueryInfluencers influencers,
+			PluralAttributeMapping attributeMapping,
+			SessionFactoryImplementor factory) {
+		final Dialect dialect = factory.getJdbcServices().getDialect();
+		final int columnCount = attributeMapping.getKeyDescriptor().getJdbcTypeCount();
+		if ( columnCount == 1
+				&& dialect.supportsStandardArrays()
+				&& dialect.getPreferredSqlTypeCodeForArray() == SqlTypes.ARRAY ) {
+			// we can use a single ARRAY parameter to send all the ids
+			return new CollectionBatchLoaderArrayParam( domainBatchSize, influencers, attributeMapping, factory );
+		}
+
+		return new CollectionBatchLoaderInPredicate( domainBatchSize, influencers, attributeMapping, factory );
+	}
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/AfterLoadAction.java

@@ -7,11 +7,25 @@
 package org.hibernate.loader.ast.spi;
 
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
-import org.hibernate.persister.entity.Loadable;
+import org.hibernate.metamodel.mapping.EntityMappingType;
 
 /**
+ * An action to be performed after an entity has been loaded.  E.g. applying locks
+ *
 * @author Steve Ebersole
 */
 public interface AfterLoadAction {
-	void afterLoad(SharedSessionContractImplementor session, Object entity, Loadable persister);
+	/**
+	 * The action trigger - the {@code entity} is being loaded
+	 */
+	void afterLoad(Object entity, EntityMappingType entityMappingType, SharedSessionContractImplementor session);
+
+	/**
+	 * @deprecated Use the {@linkplain #afterLoad(Object, EntityMappingType, SharedSessionContractImplementor) updated form}
+	 */
+	@SuppressWarnings("removal")
+	@Deprecated(since = "6", forRemoval = true)
+	default void afterLoad(SharedSessionContractImplementor session, Object entity, org.hibernate.persister.entity.Loadable persister) {
+		afterLoad( entity, persister, session );
+	}
 }

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/BatchLoader.java

@@ -0,0 +1,19 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+/**
+ * Commonality for loading a {@linkplain Loadable loadable} in "batch" (more than one key at a time)
+ *
+ * @author Steve Ebersole
+ */
+public interface BatchLoader extends MultiKeyLoader {
+	/**
+	 * The total number of {@linkplain Loadable loadable} references that can be initialized per each load operation.
+	 */
+	int getDomainBatchSize();
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/BatchLoaderFactory.java

@@ -0,0 +1,44 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+import org.hibernate.engine.spi.LoadQueryInfluencers;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.metamodel.mapping.EntityMappingType;
+import org.hibernate.metamodel.mapping.PluralAttributeMapping;
+import org.hibernate.service.Service;
+
+/**
+ * Factory for {@link BatchLoader} instances
+ *
+ * @author Steve Ebersole
+ */
+public interface BatchLoaderFactory extends Service {
+	/**
+	 * Create a BatchLoader for batch-loadable entities.
+	 *
+	 * @param domainBatchSize The total number of entities (max) that will be need to be initialized
+	 * @param entityDescriptor The entity mapping metadata
+	 */
+	<T> EntityBatchLoader<T> createEntityBatchLoader(
+			int domainBatchSize,
+			EntityMappingType entityDescriptor,
+			SessionFactoryImplementor factory);
+
+	/**
+	 * Create a BatchLoader for batch-loadable collections.
+	 *
+	 * @param domainBatchSize The total number of collections (max) that will be initialized for any {@link CollectionBatchLoader#load}
+	 * @param influencers Any load query influencers (filters, fetch-profiles, ...) to apply to the SQL
+	 * @param attributeMapping The collection mapping metadata
+	 */
+	CollectionBatchLoader createCollectionBatchLoader(
+			int domainBatchSize,
+			LoadQueryInfluencers influencers,
+			PluralAttributeMapping attributeMapping,
+			SessionFactoryImplementor factory);
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/CollectionBatchLoader.java

@@ -0,0 +1,15 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+/**
+ * BatchLoader specialization for {@linkplain org.hibernate.metamodel.mapping.PluralAttributeMapping collection} fetching
+ *
+ * @author Steve Ebersole
+ */
+public interface CollectionBatchLoader extends BatchLoader, CollectionLoader {
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/EntityBatchLoader.java

@@ -0,0 +1,15 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+/**
+ * BatchLoader specialization for {@linkplain org.hibernate.metamodel.mapping.EntityMappingType entity} fetching
+ *
+ * @author Steve Ebersole
+ */
+public interface EntityBatchLoader<T> extends BatchLoader, SingleIdEntityLoader<T> {
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/EntityMultiLoader.java

@@ -7,9 +7,9 @@
 package org.hibernate.loader.ast.spi;
 
 /**
- * Commonality for multi-loading
+ * Commonality for multi-loading an {@linkplain org.hibernate.metamodel.mapping.EntityMappingType entity}
  *
  * @param <T> The loaded model part
  */
-public interface MultiLoader<T> extends EntityLoader {
+public interface EntityMultiLoader<T> extends EntityLoader, MultiKeyLoader {
 }

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/Loadable.java

@@ -28,6 +28,19 @@ public interface Loadable extends ModelPart, RootTableGroupProducer {
 	 */
 	String getRootPathName();
 
+	default boolean isAffectedByInfluencers(LoadQueryInfluencers influencers) {
+		return isAffectedByEntityGraph( influencers )
+				|| isAffectedByEnabledFetchProfiles( influencers )
+				|| isAffectedByEnabledFilters( influencers );
+	}
+
+	default boolean isNotAffectedByInfluencers(LoadQueryInfluencers influencers) {
+		return !isAffectedByEntityGraph( influencers )
+				&& !isAffectedByEnabledFetchProfiles( influencers )
+				&& !isAffectedByEnabledFilters( influencers )
+				&& influencers.getEnabledCascadingFetchProfile() == null;
+	}
+
 	/**
 	 * Whether any of the "influencers" affect this loadable.
 	 */

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/MultiIdEntityLoader.java

@@ -8,13 +8,12 @@ package org.hibernate.loader.ast.spi;
 
 import java.util.List;
 
-import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.event.spi.EventSource;
 
 /**
  * Loader subtype for loading multiple entities by multiple identifier values.
  */
-public interface MultiIdEntityLoader<T> extends MultiLoader<T> {
+public interface MultiIdEntityLoader<T> extends EntityMultiLoader<T> {
 	/**
 	 * Load multiple entities by id.  The exact result depends on the passed options.
 	 */

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/MultiKeyLoadSizingStrategy.java

@@ -0,0 +1,50 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+import org.hibernate.dialect.Dialect;
+
+/**
+ * Strategy for determining an optimal size for loading by multiple keys.  The
+ * optimal size is defined as the most appropriate number of key values to load
+ * in any single SQL query.
+ *
+ * @apiNote This is used with IN-list style loading to determine the number
+ * of keys to encode into the SQL restriction to make sure we do not exceed
+ * database/driver limits on the number of JDBC parameters.  Generally, prefer
+ * using a SQL ARRAY parameter for the keys instead if the database/driver
+ * supports it.
+ *
+ * @see Dialect#getMultiKeyLoadSizingStrategy()
+ * @see org.hibernate.annotations.BatchSize
+ * @see org.hibernate.Session#byMultipleIds
+ * @see org.hibernate.Session#byMultipleNaturalId
+ *
+ * @author Steve Ebersole
+ */
+@FunctionalInterface
+public interface MultiKeyLoadSizingStrategy {
+	/**
+	 * Determine the optimal batch size (number of key values) to load at a time.
+	 * <p/>
+	 * The return can be less than the total {@code numberOfKeys} to be loaded indicating
+	 * that the load should be split across multiple SQL queries.  E.g. if we are loading
+	 * 7 keys and the strategy says the optimal size is 5, we will perform 2 queries.
+	 * <p/>
+	 * @apiNote
+	 *
+	 * @param numberOfKeyColumns The number of columns to which the key is mapped
+	 * @param numberOfKeys The total number of keys we need to load
+	 * @param inClauseParameterPaddingEnabled See {@link org.hibernate.cfg.AvailableSettings#IN_CLAUSE_PARAMETER_PADDING}
+	 *
+	 * @return The number of keys to load at once.  The total number of JDBC parameters needed for that load is
+	 * defined by {@code numberOfKeys} * {@code numberOfKeyColumns}. The strategy should take care to ensure that
+	 * {@code numberOfKeys} * {@code numberOfKeyColumns} does not exceed any database/driver limits on the number
+	 * of parameters allowed in a {@linkplain java.sql.PreparedStatement}.
+	 */
+	int determineOptimalBatchLoadSize(int numberOfKeyColumns, int numberOfKeys, boolean inClauseParameterPaddingEnabled);
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/MultiKeyLoader.java

@@ -0,0 +1,16 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+/**
+ * Loader specialization for loading multiple {@linkplain Loadable loadable}
+ * references by primary, foreign or natural key.
+ *
+ * @author Steve Ebersole
+ */
+public interface MultiKeyLoader extends Loader {
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/MultiNaturalIdLoader.java

@@ -15,7 +15,7 @@ import org.hibernate.engine.spi.SharedSessionContractImplementor;
  *
  * @param <E> The entity Java type
  */
-public interface MultiNaturalIdLoader<E> extends MultiLoader<E> {
+public interface MultiNaturalIdLoader<E> extends EntityMultiLoader<E> {
 	/**
 	 * Load multiple entities by natural-id.  The exact result depends on the passed options.
 	 *

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/NaturalIdLoader.java

@@ -13,7 +13,7 @@ import org.hibernate.engine.spi.SharedSessionContractImplementor;
  *
  * @author Steve Ebersole
  */
-public interface NaturalIdLoader<T> extends EntityLoader {
+public interface NaturalIdLoader<T> extends EntityLoader, MultiKeyLoader {
 
 	/**
 	 * Perform the load of the entity by its natural-id

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/SqlArrayMultiKeyLoader.java

@@ -0,0 +1,17 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+/**
+ * MultiKeyLoader implementation based on a SQL ARRAY valued parameter
+ *
+ * @see SqlInPredicateMultiKeyLoader
+ *
+ * @author Steve Ebersole
+ */
+public interface SqlArrayMultiKeyLoader extends MultiKeyLoader {
+}

hibernate-core/src/main/java/org/hibernate/loader/ast/spi/SqlInPredicateMultiKeyLoader.java

@@ -0,0 +1,17 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.loader.ast.spi;
+
+/**
+ * MultiKeyLoader implementation based on SQL IN predicate
+ *
+ * @see SqlArrayMultiKeyLoader
+ *
+ * @author Steve Ebersole
+ */
+public interface SqlInPredicateMultiKeyLoader extends MultiKeyLoader {
+}

hibernate-core/src/main/java/org/hibernate/mapping/MappingHelper.java

@@ -17,7 +17,7 @@ import org.hibernate.boot.registry.classloading.spi.ClassLoaderService;
 import org.hibernate.boot.spi.MetadataBuildingContext;
 import org.hibernate.boot.spi.MetadataImplementor;
 import org.hibernate.internal.util.collections.CollectionHelper;
-import org.hibernate.metamodel.mapping.MappingModelCreationLogger;
+import org.hibernate.metamodel.mapping.MappingModelCreationLogging;
 import org.hibernate.resource.beans.internal.FallbackBeanInstanceProducer;
 import org.hibernate.resource.beans.spi.ManagedBean;
 import org.hibernate.resource.beans.spi.ManagedBeanRegistry;
@@ -34,6 +34,8 @@ import org.hibernate.type.Type;
 import org.hibernate.usertype.ParameterizedType;
 import org.hibernate.usertype.UserCollectionType;
 
+import static org.hibernate.metamodel.mapping.MappingModelCreationLogging.MAPPING_MODEL_CREATION_MESSAGE_LOGGER;
+
 /**
  * @author Steve Ebersole
  */
@@ -107,7 +109,7 @@ public final class MappingHelper {
 			( (ParameterizedType) type ).setParameterValues( parameters == null ? EMPTY_PROPERTIES : parameters );
 		}
 		else if ( parameters != null && !parameters.isEmpty() ) {
-			MappingModelCreationLogger.LOGGER.debugf(
+			MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf(
 					"UserCollectionType impl does not implement ParameterizedType but parameters were present : `%s`",
 					type.getClass().getName()
 			);

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/MappingModelCreationLogging.java

@@ -21,14 +21,15 @@ import org.jboss.logging.annotations.ValidIdRange;
 @MessageLogger( projectCode = "HHH" )
 @ValidIdRange( min = 90005701, max = 90005800 )
 @SubSystemLogging(
-		name = MappingModelCreationLogger.LOGGER_NAME,
+		name = MappingModelCreationLogging.LOGGER_NAME,
 		description = "Logging related to building of Hibernate's runtime metamodel descriptors of the domain model"
 )
-public interface MappingModelCreationLogger extends BasicLogger {
+public interface MappingModelCreationLogging extends BasicLogger {
 	String LOGGER_NAME = SubSystemLogging.BASE + ".model.mapping.creation";
 
-	MappingModelCreationLogger LOGGER = Logger.getMessageLogger( MappingModelCreationLogger.class, LOGGER_NAME );
+	Logger MAPPING_MODEL_CREATION_LOGGER = Logger.getLogger( LOGGER_NAME );
+	MappingModelCreationLogging MAPPING_MODEL_CREATION_MESSAGE_LOGGER = Logger.getMessageLogger( MappingModelCreationLogging.class, LOGGER_NAME );
 
-	boolean TRACE_ENABLED = LOGGER.isTraceEnabled();
+	boolean MAPPING_MODEL_CREATION_TRACE_ENABLED = MAPPING_MODEL_CREATION_LOGGER.isTraceEnabled();
-	boolean DEBUG_ENABLED = LOGGER.isDebugEnabled();
+	boolean MAPPING_MODEL_CREATION_DEBUG_ENABLED = MAPPING_MODEL_CREATION_LOGGER.isDebugEnabled();
 }

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/CompoundNaturalIdMapping.java

@@ -20,7 +20,7 @@ import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.internal.util.IndexedConsumer;
 import org.hibernate.loader.ast.internal.CompoundNaturalIdLoader;
-import org.hibernate.loader.ast.internal.MultiNaturalIdLoaderStandard;
+import org.hibernate.loader.ast.internal.MultiNaturalIdLoaderInPredicate;
 import org.hibernate.loader.ast.spi.MultiNaturalIdLoader;
 import org.hibernate.loader.ast.spi.NaturalIdLoader;
 import org.hibernate.metamodel.UnsupportedMappingException;
@@ -251,7 +251,7 @@ public class CompoundNaturalIdMapping extends AbstractNaturalIdMapping implement
 
 	@Override
 	public MultiNaturalIdLoader<?> makeMultiLoader(EntityMappingType entityDescriptor) {
-		return new MultiNaturalIdLoaderStandard<>( entityDescriptor );
+		return new MultiNaturalIdLoaderInPredicate<>( entityDescriptor );
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/MappingModelCreationHelper.java

@@ -62,7 +62,6 @@ import org.hibernate.metamodel.mapping.EntityIdentifierMapping;
 import org.hibernate.metamodel.mapping.ForeignKeyDescriptor;
 import org.hibernate.metamodel.mapping.JdbcMapping;
 import org.hibernate.metamodel.mapping.ManagedMappingType;
-import org.hibernate.metamodel.mapping.MappingModelCreationLogger;
 import org.hibernate.metamodel.mapping.ModelPart;
 import org.hibernate.metamodel.mapping.ModelPartContainer;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
@@ -101,7 +100,8 @@ import org.hibernate.type.descriptor.java.MutabilityPlan;
 import org.hibernate.type.descriptor.java.spi.JavaTypeRegistry;
 import org.hibernate.type.spi.TypeConfiguration;
 
-import static org.hibernate.metamodel.mapping.MappingModelCreationLogger.LOGGER;
+import static org.hibernate.metamodel.mapping.MappingModelCreationLogging.MAPPING_MODEL_CREATION_DEBUG_ENABLED;
+import static org.hibernate.metamodel.mapping.MappingModelCreationLogging.MAPPING_MODEL_CREATION_MESSAGE_LOGGER;
 import static org.hibernate.sql.ast.spi.SqlExpressionResolver.createColumnReferenceKey;
 
 /**
@@ -208,7 +208,7 @@ public class MappingModelCreationHelper {
 		final FetchStyle fetchStyle;
 		if ( declaringType instanceof EmbeddableMappingType ) {
 			if ( bootProperty.isLazy() ) {
-				LOGGER.debugf(
+				MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf(
 						"Attribute was declared lazy, but is part of an embeddable - `%s#%s` - LAZY will be ignored",
 						declaringType.getNavigableRole().getFullPath(),
 						bootProperty.getName()
@@ -656,24 +656,23 @@ public class MappingModelCreationHelper {
 				sessionFactory
 		);
 
-		final PluralAttributeMappingImpl pluralAttributeMapping = mappingConverter
+		final PluralAttributeMappingImpl pluralAttributeMapping = mappingConverter.apply( new PluralAttributeMappingImpl(
-				.apply( new PluralAttributeMappingImpl(
+				attrName,
-						attrName,
+				bootValueMapping,
-						bootValueMapping,
+				propertyAccess,
-						propertyAccess,
+				attributeMetadata,
-						attributeMetadata,
+				collectionMappingType,
-						collectionMappingType,
+				stateArrayPosition,
-						stateArrayPosition,
+				fetchableIndex,
-						fetchableIndex,
+				elementDescriptor,
-						elementDescriptor,
+				indexDescriptor,
-						indexDescriptor,
+				identifierDescriptor,
-						identifierDescriptor,
+				timing,
-						timing,
+				style,
-						style,
+				cascadeStyle,
-						cascadeStyle,
+				declaringType,
-						declaringType,
+				collectionDescriptor
-						collectionDescriptor
+		) );
-				) );
 
 		creationProcess.registerInitializationCallback(
 				"PluralAttributeMapping(" + bootValueMapping.getRole() + ")#finishInitialization",
@@ -1695,8 +1694,8 @@ public class MappingModelCreationHelper {
 					|| value instanceof ManyToOne && value.isNullable() && ( (ManyToOne) value ).isIgnoreNotFound() ) {
 				fetchTiming = FetchTiming.IMMEDIATE;
 				if ( lazy ) {
-					if ( MappingModelCreationLogger.DEBUG_ENABLED ) {
+					if ( MAPPING_MODEL_CREATION_DEBUG_ENABLED ) {
-						MappingModelCreationLogger.LOGGER.debugf(
+						MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf(
 								"Forcing FetchTiming.IMMEDIATE for to-one association : %s.%s",
 								declaringType.getNavigableRole(),
 								bootProperty.getName()

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/MappingModelCreationProcess.java

@@ -13,7 +13,6 @@ import java.util.Map;
 import java.util.function.Consumer;
 
 import org.hibernate.metamodel.mapping.ForeignKeyDescriptor;
-import org.hibernate.metamodel.mapping.MappingModelCreationLogger;
 import org.hibernate.metamodel.mapping.ModelPart;
 import org.hibernate.metamodel.mapping.NonTransientException;
 import org.hibernate.metamodel.model.domain.NavigableRole;
@@ -21,6 +20,9 @@ import org.hibernate.metamodel.spi.RuntimeModelCreationContext;
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.query.sqm.function.SqmFunctionRegistry;
 
+import static org.hibernate.metamodel.mapping.MappingModelCreationLogging.MAPPING_MODEL_CREATION_MESSAGE_LOGGER;
+import static org.hibernate.metamodel.mapping.MappingModelCreationLogging.MAPPING_MODEL_CREATION_TRACE_ENABLED;
+
 /**
  * @author Steve Ebersole
  */
@@ -41,11 +43,9 @@ public class MappingModelCreationProcess {
 	}
 
 	private final Map<String,EntityPersister> entityPersisterMap;
-
 	private final RuntimeModelCreationContext creationContext;
 
 	private String currentlyProcessingRole;
-
 	private List<PostInitCallbackEntry> postInitCallbacks;
 
 	private MappingModelCreationProcess(
@@ -89,7 +89,7 @@ public class MappingModelCreationProcess {
 	}
 
 	private void executePostInitCallbacks() {
-		MappingModelCreationLogger.LOGGER.debugf( "Starting post-init callbacks" );
+		MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf( "Starting post-init callbacks" );
 
 		Map<PostInitCallbackEntry, Exception> exceptions = new HashMap<>();
 		while ( postInitCallbacks != null && !postInitCallbacks.isEmpty() ) {
@@ -112,7 +112,7 @@ public class MappingModelCreationProcess {
 				}
 				catch (Exception e) {
 					if ( e instanceof NonTransientException ) {
-						MappingModelCreationLogger.LOGGER.debugf(
+						MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf(
 								"Mapping-model creation encountered non-transient error : %s",
 								e
 						);
@@ -121,11 +121,11 @@ public class MappingModelCreationProcess {
 					exceptions.put( callbackEntry, e );
 
 					final String format = "Mapping-model creation encountered (possibly) transient error : %s";
-					if ( MappingModelCreationLogger.TRACE_ENABLED ) {
+					if ( MAPPING_MODEL_CREATION_TRACE_ENABLED ) {
-						MappingModelCreationLogger.LOGGER.tracef( e, format, e );
+						MAPPING_MODEL_CREATION_MESSAGE_LOGGER.tracef( e, format, e );
 					}
 					else {
-						MappingModelCreationLogger.LOGGER.debugf( format, e );
+						MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf( format, e );
 					}
 				}
 			}
@@ -239,7 +239,7 @@ public class MappingModelCreationProcess {
 		}
 
 		private boolean process() {
-			MappingModelCreationLogger.LOGGER.debugf(
+			MAPPING_MODEL_CREATION_MESSAGE_LOGGER.debugf(
 					"Starting PostInitCallbackEntry : %s",
 					description
 			);

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/PluralAttributeMappingImpl.java

@@ -13,6 +13,7 @@ import java.util.function.Supplier;
 import org.hibernate.cache.MutableCacheKeyBuilder;
 import org.hibernate.engine.FetchStyle;
 import org.hibernate.engine.FetchTiming;
+import org.hibernate.engine.profile.internal.FetchProfileAffectee;
 import org.hibernate.engine.spi.CascadeStyle;
 import org.hibernate.engine.spi.LoadQueryInfluencers;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
@@ -75,7 +76,7 @@ import org.jboss.logging.Logger;
  */
 public class PluralAttributeMappingImpl
 		extends AbstractAttributeMapping
-		implements PluralAttributeMapping, FetchOptions {
+		implements PluralAttributeMapping, FetchProfileAffectee, FetchOptions {
 	private static final Logger log = Logger.getLogger( PluralAttributeMappingImpl.class );
 
 	/**
@@ -894,6 +895,13 @@ public class PluralAttributeMappingImpl
 		return getCollectionDescriptor().isAffectedByEntityGraph( influencers );
 	}
 
+	@Override
+	public void registerAffectingFetchProfile(String fetchProfileName, org.hibernate.engine.profile.Fetch.Style fetchStyle) {
+		if ( collectionDescriptor instanceof FetchProfileAffectee ) {
+			( (FetchProfileAffectee) collectionDescriptor ).registerAffectingFetchProfile( fetchProfileName, fetchStyle );
+		}
+	}
+
 	@Override
 	public boolean isAffectedByEnabledFetchProfiles(LoadQueryInfluencers influencers) {
 		return getCollectionDescriptor().isAffectedByEnabledFetchProfiles( influencers );

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/SimpleNaturalIdMapping.java

@@ -15,18 +15,13 @@ import java.util.function.BiConsumer;
 import org.hibernate.HibernateException;
 import org.hibernate.cache.MutableCacheKeyBuilder;
 import org.hibernate.engine.spi.PersistenceContext;
+import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.internal.util.IndexedConsumer;
-import org.hibernate.loader.ast.internal.MultiNaturalIdLoaderStandard;
+import org.hibernate.loader.ast.internal.*;
-import org.hibernate.loader.ast.internal.SimpleNaturalIdLoader;
 import org.hibernate.loader.ast.spi.MultiNaturalIdLoader;
 import org.hibernate.loader.ast.spi.NaturalIdLoader;
-import org.hibernate.metamodel.mapping.AttributeMapping;
+import org.hibernate.metamodel.mapping.*;
-import org.hibernate.metamodel.mapping.EntityMappingType;
-import org.hibernate.metamodel.mapping.JdbcMapping;
-import org.hibernate.metamodel.mapping.MappingType;
-import org.hibernate.metamodel.mapping.SelectableConsumer;
-import org.hibernate.metamodel.mapping.SingularAttributeMapping;
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.spi.NavigablePath;
 import org.hibernate.sql.ast.spi.SqlSelection;
@@ -36,11 +31,14 @@ import org.hibernate.sql.results.graph.DomainResultCreationState;
 import org.hibernate.type.descriptor.java.JavaType;
 import org.hibernate.type.spi.TypeConfiguration;
 
+import static org.hibernate.loader.ast.internal.MultiKeyLoadHelper.supportsSqlArrayType;
+
 /**
  * Single-attribute NaturalIdMapping implementation
  */
 public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements JavaType.CoercionContext {
 	private final SingularAttributeMapping attribute;
+	private final SessionFactoryImplementor sessionFactory;
 	private final TypeConfiguration typeConfiguration;
 
 	public SimpleNaturalIdMapping(
@@ -53,7 +51,8 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 		);
 		this.attribute = attribute;
 
-		typeConfiguration = creationProcess.getCreationContext().getTypeConfiguration();
+		this.sessionFactory = creationProcess.getCreationContext().getSessionFactory();
+		this.typeConfiguration = creationProcess.getCreationContext().getTypeConfiguration();
 
 	}
 
@@ -62,7 +61,11 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 	}
 
 	@Override
-	public void verifyFlushState(Object id, Object[] currentState, Object[] loadedState, SharedSessionContractImplementor session) {
+	public void verifyFlushState(
+			Object id,
+			Object[] currentState,
+			Object[] loadedState,
+			SharedSessionContractImplementor session) {
 		if ( isMutable() ) {
 			// EARLY EXIT!!!
 			// the natural id is mutable (!immutable), no need to do the checks
@@ -77,7 +80,7 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 				? persistenceContext.getNaturalIdSnapshot( id, persister )
 				: persister.getNaturalIdMapping().extractNaturalIdFromEntityState( loadedState );
 
-		if ( ! areEqual( naturalId, snapshot, session ) ) {
+		if ( !areEqual( naturalId, snapshot, session ) ) {
 			throw new HibernateException(
 					String.format(
 							"An immutable natural identifier of entity %s was altered from `%s` to `%s`",
@@ -99,7 +102,7 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 			return state[0];
 		}
 
-		return state[ attribute.getStateArrayPosition() ];
+		return state[attribute.getStateArrayPosition()];
 	}
 
 	@Override
@@ -122,7 +125,7 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 			}
 		}
 
-		if ( ! getJavaType().getJavaTypeClass().isInstance( naturalIdValue ) ) {
+		if ( !getJavaType().getJavaTypeClass().isInstance( naturalIdValue ) ) {
 			throw new IllegalArgumentException(
 					String.format(
 							Locale.ROOT,
@@ -146,7 +149,7 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 		return normalizeIncomingValue( incoming );
 	}
 
-	@SuppressWarnings( "rawtypes" )
+	@SuppressWarnings("rawtypes")
 	public Object normalizeIncomingValue(Object naturalIdToLoad) {
 		final Object normalizedValue;
 		if ( naturalIdToLoad instanceof Map ) {
@@ -195,7 +198,10 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 	}
 
 	@Override
-	public void applySqlSelections(NavigablePath navigablePath, TableGroup tableGroup, DomainResultCreationState creationState) {
+	public void applySqlSelections(
+			NavigablePath navigablePath,
+			TableGroup tableGroup,
+			DomainResultCreationState creationState) {
 		attribute.applySqlSelections( navigablePath, tableGroup, creationState );
 	}
 
@@ -288,7 +294,11 @@ public class SimpleNaturalIdMapping extends AbstractNaturalIdMapping implements
 
 	@Override
 	public MultiNaturalIdLoader<?> makeMultiLoader(EntityMappingType entityDescriptor) {
-		return new MultiNaturalIdLoaderStandard<>( entityDescriptor );
+		boolean supportsSqlArrayType = supportsSqlArrayType( sessionFactory.getFastSessionServices().jdbcServices.getDialect() );
+		if ( supportsSqlArrayType && attribute instanceof BasicAttributeMapping ) {
+			return new MultiNaturalIdLoaderArrayParam<>( entityDescriptor );
+		}
+		return new MultiNaturalIdLoaderInPredicate<>( entityDescriptor );
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/persister/collection/AbstractCollectionPersister.java

@@ -41,7 +41,7 @@ import org.hibernate.engine.jdbc.mutation.internal.MutationQueryOptions;
 import org.hibernate.engine.jdbc.spi.JdbcCoordinator;
 import org.hibernate.engine.jdbc.spi.SqlExceptionHelper;
 import org.hibernate.engine.profile.Fetch;
-import org.hibernate.engine.profile.FetchProfile;
+import org.hibernate.engine.profile.internal.FetchProfileAffectee;
 import org.hibernate.engine.spi.EntityKey;
 import org.hibernate.engine.spi.ExecuteUpdateResultCheckStyle;
 import org.hibernate.engine.spi.LoadQueryInfluencers;
@@ -58,11 +58,11 @@ import org.hibernate.internal.util.StringHelper;
 import org.hibernate.jdbc.Expectation;
 import org.hibernate.jdbc.Expectations;
 import org.hibernate.loader.ast.internal.CollectionElementLoaderByIndex;
-import org.hibernate.loader.ast.internal.CollectionLoaderBatchKey;
 import org.hibernate.loader.ast.internal.CollectionLoaderNamedQuery;
 import org.hibernate.loader.ast.internal.CollectionLoaderSingleKey;
 import org.hibernate.loader.ast.internal.CollectionLoaderSubSelectFetch;
 import org.hibernate.loader.ast.internal.LoaderSqlAstCreationState;
+import org.hibernate.loader.ast.spi.BatchLoaderFactory;
 import org.hibernate.loader.ast.spi.CollectionLoader;
 import org.hibernate.mapping.Collection;
 import org.hibernate.mapping.Column;
@@ -145,7 +145,7 @@ import static org.hibernate.sql.model.ModelMutationLogging.MODEL_MUTATION_LOGGER
  */
 @Internal
 public abstract class AbstractCollectionPersister
-		implements CollectionPersister, CollectionMutationTarget, PluralAttributeMappingImpl.Aware, DeprecatedCollectionStuff {
+		implements CollectionPersister, CollectionMutationTarget, PluralAttributeMappingImpl.Aware, FetchProfileAffectee, DeprecatedCollectionStuff {
 
 	private final NavigableRole navigableRole;
 	private final CollectionSemantics<?,?> collectionSemantics;
@@ -232,6 +232,7 @@ public abstract class AbstractCollectionPersister
 	private CollectionElementLoaderByIndex collectionElementLoaderByIndex;
 
 	private PluralAttributeMapping attributeMapping;
+	private volatile Map<String, Fetch.Style> affectingFetchProfiles;
 
 
 	@Deprecated(since = "6.0")
@@ -738,13 +739,32 @@ public abstract class AbstractCollectionPersister
 		);
 	}
 
+	private CollectionLoader reusableCollectionLoader;
+
 	protected CollectionLoader createCollectionLoader(LoadQueryInfluencers loadQueryInfluencers) {
-		final int batchSize = getBatchSize();
+		if ( canUseReusableCollectionLoader( loadQueryInfluencers ) ) {
-		if ( batchSize > 1 ) {
+			if ( reusableCollectionLoader == null ) {
-			return new CollectionLoaderBatchKey( attributeMapping, batchSize, loadQueryInfluencers, getFactory() );
+				reusableCollectionLoader = generateCollectionLoader( LoadQueryInfluencers.NONE );
+			}
+			return reusableCollectionLoader;
 		}
 
+		// create a one-off
+		return generateCollectionLoader( loadQueryInfluencers );
+	}
 
+	private boolean canUseReusableCollectionLoader(LoadQueryInfluencers loadQueryInfluencers) {
+		// we can reuse it so long as none of the enabled influencers affect it
+		return attributeMapping.isNotAffectedByInfluencers( loadQueryInfluencers );
+	}
+
+	private CollectionLoader generateCollectionLoader(LoadQueryInfluencers loadQueryInfluencers) {
+		final int batchSize = getBatchSize();
+		if ( batchSize > 1 ) {
+			return getFactory().getServiceRegistry()
+					.getService( BatchLoaderFactory.class )
+					.createCollectionBatchLoader( batchSize, loadQueryInfluencers, attributeMapping, getFactory() );
+		}
 		return new CollectionLoaderSingleKey( attributeMapping, loadQueryInfluencers, getFactory() );
 	}
 
@@ -1502,6 +1522,29 @@ public abstract class AbstractCollectionPersister
 		return attributeMapping;
 	}
 
+	@Override
+	public void registerAffectingFetchProfile(String fetchProfileName, Fetch.Style fetchStyle) {
+		if ( affectingFetchProfiles == null ) {
+			affectingFetchProfiles = new HashMap<>();
+		}
+		affectingFetchProfiles.put( fetchProfileName, fetchStyle );
+	}
+
+	@Override
+	public boolean isAffectedByEnabledFetchProfiles(LoadQueryInfluencers influencers) {
+		if ( affectingFetchProfiles == null ) {
+			return false;
+		}
+
+		for ( Map.Entry<String, Fetch.Style> entry : affectingFetchProfiles.entrySet() ) {
+			if ( influencers.isFetchProfileEnabled( entry.getKey() ) ) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	@Override
 	public boolean isAffectedByEnabledFilters(LoadQueryInfluencers influencers) {
 		if ( influencers.hasEnabledFilters() ) {
@@ -1519,21 +1562,6 @@ public abstract class AbstractCollectionPersister
 		return false;
 	}
 
-	@Override
-	public boolean isAffectedByEnabledFetchProfiles(LoadQueryInfluencers influencers) {
-		if ( influencers.hasEnabledFetchProfiles() ) {
-			for ( String enabledFetchProfileName : influencers.getEnabledFetchProfileNames() ) {
-				final FetchProfile fetchProfile = getFactory().getFetchProfile( enabledFetchProfileName );
-				final Fetch fetch = fetchProfile.getFetchByRole( getRole() );
-				if ( fetch != null && fetch.getStyle() == Fetch.Style.JOIN ) {
-					return true;
-				}
-			}
-		}
-
-		return false;
-	}
-
 	@Override
 	public CollectionSemantics<?,?> getCollectionSemantics() {
 		return collectionSemantics;

hibernate-core/src/main/java/org/hibernate/persister/entity/AbstractEntityPersister.java

@@ -75,6 +75,7 @@ import org.hibernate.engine.internal.MutableEntityEntryFactory;
 import org.hibernate.engine.internal.StatefulPersistenceContext;
 import org.hibernate.engine.jdbc.mutation.spi.MutationExecutorService;
 import org.hibernate.engine.jdbc.spi.JdbcCoordinator;
+import org.hibernate.engine.jdbc.spi.JdbcServices;
 import org.hibernate.engine.spi.CachedNaturalIdValueSource;
 import org.hibernate.engine.spi.CascadeStyle;
 import org.hibernate.engine.spi.CollectionKey;
@@ -116,16 +117,19 @@ import org.hibernate.internal.util.collections.ArrayHelper;
 import org.hibernate.internal.util.collections.LockModeEnumMap;
 import org.hibernate.jdbc.Expectation;
 import org.hibernate.jdbc.TooManyRowsAffectedException;
+import org.hibernate.loader.ast.internal.MultiKeyLoadHelper;
 import org.hibernate.loader.ast.internal.CacheEntityLoaderHelper;
+import org.hibernate.engine.profile.internal.FetchProfileAffectee;
 import org.hibernate.loader.ast.internal.LoaderSelectBuilder;
 import org.hibernate.loader.ast.internal.LoaderSqlAstCreationState;
-import org.hibernate.loader.ast.internal.MultiIdLoaderStandard;
+import org.hibernate.loader.ast.internal.MultiIdEntityLoaderArrayParam;
+import org.hibernate.loader.ast.internal.MultiIdEntityLoaderStandard;
 import org.hibernate.loader.ast.internal.Preparable;
 import org.hibernate.loader.ast.internal.SingleIdArrayLoadPlan;
-import org.hibernate.loader.ast.internal.SingleIdEntityLoaderDynamicBatch;
 import org.hibernate.loader.ast.internal.SingleIdEntityLoaderProvidedQueryImpl;
 import org.hibernate.loader.ast.internal.SingleIdEntityLoaderStandardImpl;
 import org.hibernate.loader.ast.internal.SingleUniqueKeyEntityLoaderStandard;
+import org.hibernate.loader.ast.spi.BatchLoaderFactory;
 import org.hibernate.loader.ast.spi.Loader;
 import org.hibernate.loader.ast.spi.MultiIdEntityLoader;
 import org.hibernate.loader.ast.spi.MultiIdLoadOptions;
@@ -309,7 +313,7 @@ import static org.hibernate.sql.ast.spi.SqlExpressionResolver.createColumnRefere
  */
 @Internal
 public abstract class AbstractEntityPersister
-		implements InFlightEntityMappingType, EntityMutationTarget, LazyPropertyInitializer, PostInsertIdentityPersister, DeprecatedEntityStuff {
+		implements InFlightEntityMappingType, EntityMutationTarget, LazyPropertyInitializer, PostInsertIdentityPersister, FetchProfileAffectee, DeprecatedEntityStuff {
 
 	private static final CoreMessageLogger LOG = CoreLogging.messageLogger( AbstractEntityPersister.class );
 
@@ -322,8 +326,8 @@ public abstract class AbstractEntityPersister
 
 	private final String sqlAliasStem;
 
-	private final SingleIdEntityLoader<?> singleIdEntityLoader;
+	private final SingleIdEntityLoader<?> singleIdLoader;
-	private final MultiIdEntityLoader<?> multiIdEntityLoader;
+	private final MultiIdEntityLoader<?> multiIdLoader;
 	private NaturalIdLoader<?> naturalIdLoader;
 	private MultiNaturalIdLoader<?> multiNaturalIdLoader;
 
@@ -529,16 +533,16 @@ public abstract class AbstractEntityPersister
 				throw new IllegalArgumentException( "Could not resolve named load-query [" + getEntityName()
 						+ "] : " + persistentClass.getLoaderName() );
 			}
-			singleIdEntityLoader = new SingleIdEntityLoaderProvidedQueryImpl<>( this, namedQueryMemento );
+			singleIdLoader = new SingleIdEntityLoaderProvidedQueryImpl<>( this, namedQueryMemento );
 		}
 		else if ( batchSize > 1 ) {
-			singleIdEntityLoader = createBatchingIdEntityLoader( this, batchSize, factory );
+			singleIdLoader = createBatchingIdEntityLoader( this, batchSize, factory );
 		}
 		else {
-			singleIdEntityLoader = new SingleIdEntityLoaderStandardImpl<>( this, factory );
+			singleIdLoader = new SingleIdEntityLoaderStandardImpl<>( this, factory );
 		}
 
-		multiIdEntityLoader = new MultiIdLoaderStandard<>( this, persistentClass, factory );
+		multiIdLoader = buildMultiIdLoader( persistentClass );
 
 		final TypeConfiguration typeConfiguration = creationContext.getTypeConfiguration();
 		final SqmFunctionRegistry functionRegistry = creationContext.getFunctionRegistry();
@@ -801,6 +805,14 @@ public abstract class AbstractEntityPersister
 		fullDiscriminatorValues = toObjectArray( values );
 	}
 
+	private MultiIdEntityLoader<Object> buildMultiIdLoader(PersistentClass persistentClass) {
+		if ( persistentClass.getIdentifier() instanceof BasicValue
+				&& MultiKeyLoadHelper.supportsSqlArrayType( factory.getServiceRegistry().getService( JdbcServices.class ).getDialect() ) ) {
+			return new MultiIdEntityLoaderArrayParam<>( this, factory );
+		}
+		return new MultiIdEntityLoaderStandard<>( this, persistentClass, factory );
+	}
+
 	private String getIdentitySelectString(Dialect dialect) {
 		try {
 			return dialect.getIdentityColumnSupport()
@@ -1006,13 +1018,15 @@ public abstract class AbstractEntityPersister
 
 	private static SingleIdEntityLoader<?> createBatchingIdEntityLoader(
 			EntityMappingType entityDescriptor,
-			int batchSize,
+			int domainBatchSize,
 			SessionFactoryImplementor factory) {
-		return new SingleIdEntityLoaderDynamicBatch<>( entityDescriptor, batchSize, factory );
+		return factory.getServiceRegistry()
+				.getService( BatchLoaderFactory.class )
+				.createEntityBatchLoader( domainBatchSize, entityDescriptor, factory );
 	}
 
 	/**
-	 * We might need to use cache invalidation is we have formulas,
+	 * We might need to use cache invalidation if we have formulas,
 	 * dynamic update, or secondary tables.
 	 *
 	 * @see #isCacheInvalidationRequired()
@@ -1837,7 +1851,7 @@ public abstract class AbstractEntityPersister
 
 	@Override
 	public Object[] getDatabaseSnapshot(Object id, SharedSessionContractImplementor session) throws HibernateException {
-		return singleIdEntityLoader.loadDatabaseSnapshot( id, session );
+		return singleIdLoader.loadDatabaseSnapshot( id, session );
 	}
 
 	@Override
@@ -3323,8 +3337,8 @@ public abstract class AbstractEntityPersister
 	@Override
 	public final void postInstantiate() throws MappingException {
 		doLateInit();
-		prepareLoader( singleIdEntityLoader );
+		prepareLoader( singleIdLoader );
-		prepareLoader( multiIdEntityLoader );
+		prepareLoader( multiIdLoader );
 	}
 
 	private void prepareLoader(Loader loader) {
@@ -3364,15 +3378,15 @@ public abstract class AbstractEntityPersister
 		}
 
 		if ( optionalObject == null ) {
-			return singleIdEntityLoader.load( id, lockOptions, readOnly, session );
+			return singleIdLoader.load( id, lockOptions, readOnly, session );
 		}
 		else {
-			return singleIdEntityLoader.load( id, optionalObject, lockOptions, readOnly, session );
+			return singleIdLoader.load( id, optionalObject, lockOptions, readOnly, session );
 		}
 	}
 
-	public SingleIdEntityLoader<?> getSingleIdEntityLoader() {
+	public SingleIdEntityLoader<?> getSingleIdLoader() {
-		return singleIdEntityLoader;
+		return singleIdLoader;
 	}
 
 	@Override
@@ -3394,7 +3408,7 @@ public abstract class AbstractEntityPersister
 				loaded = CacheEntityLoaderHelper.INSTANCE.loadFromSecondLevelCache( loadEvent, this, entityKey );
 			}
 			if ( loaded == null ) {
-				loaded = singleIdEntityLoader.load( identifier, entity, LockOptions.NONE, session );
+				loaded = singleIdLoader.load( identifier, entity, LockOptions.NONE, session );
 			}
 
 			if ( loaded == null ) {
@@ -3426,7 +3440,7 @@ public abstract class AbstractEntityPersister
 
 	@Override
 	public List<?> multiLoad(Object[] ids, EventSource session, MultiIdLoadOptions loadOptions) {
-		return multiIdEntityLoader.load( ids, loadOptions, session );
+		return multiIdLoader.load( ids, loadOptions, session );
 	}
 
 	@Override
@@ -3437,6 +3451,11 @@ public abstract class AbstractEntityPersister
 		affectingFetchProfileNames.add( fetchProfileName );
 	}
 
+	@Override
+	public void registerAffectingFetchProfile(String fetchProfileName, org.hibernate.engine.profile.Fetch.Style fetchStyle) {
+		registerAffectingFetchProfile( fetchProfileName );
+	}
+
 	@Override
 	public boolean isAffectedByEntityGraph(LoadQueryInfluencers loadQueryInfluencers) {
 		final RootGraphImplementor<?> graph = loadQueryInfluencers.getEffectiveEntityGraph().getGraph();

hibernate-core/src/main/java/org/hibernate/service/StandardServiceInitiators.java

@@ -32,6 +32,7 @@ import org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiat
 import org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformResolverInitiator;
 import org.hibernate.event.internal.EntityCopyObserverFactoryInitiator;
 import org.hibernate.id.factory.internal.StandardIdentifierGeneratorFactoryInitiator;
+import org.hibernate.loader.ast.internal.BatchLoaderFactoryInitiator;
 import org.hibernate.persister.internal.PersisterClassResolverInitiator;
 import org.hibernate.persister.internal.PersisterFactoryInitiator;
 import org.hibernate.property.access.internal.PropertyAccessStrategyResolverInitiator;
@@ -158,6 +159,7 @@ public final class StandardServiceInitiators {
 
 		// ParameterMarkerStrategy
 		serviceInitiators.add( ParameterMarkerStrategyInitiator.INSTANCE );
+		serviceInitiators.add( BatchLoaderFactoryInitiator.INSTANCE );
 
 		serviceInitiators.trimToSize();
 

hibernate-core/src/main/java/org/hibernate/sql/ast/SqlAstWalker.java

@@ -54,6 +54,7 @@ import org.hibernate.sql.ast.tree.predicate.ComparisonPredicate;
 import org.hibernate.sql.ast.tree.predicate.ExistsPredicate;
 import org.hibernate.sql.ast.tree.predicate.FilterPredicate;
 import org.hibernate.sql.ast.tree.predicate.GroupedPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.InListPredicate;
 import org.hibernate.sql.ast.tree.predicate.InSubQueryPredicate;
 import org.hibernate.sql.ast.tree.predicate.Junction;
@@ -188,6 +189,8 @@ public interface SqlAstWalker {
 
 	void visitInSubQueryPredicate(InSubQueryPredicate inSubQueryPredicate);
 
+	void visitInArrayPredicate(InArrayPredicate inArrayPredicate);
+
 	void visitExistsPredicate(ExistsPredicate existsPredicate);
 
 	void visitJunction(Junction junction);

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/AbstractSqlAstTranslator.java

@@ -153,6 +153,7 @@ import org.hibernate.sql.ast.tree.predicate.FilterPredicate;
 import org.hibernate.sql.ast.tree.predicate.FilterPredicate.FilterFragmentParameter;
 import org.hibernate.sql.ast.tree.predicate.FilterPredicate.FilterFragmentPredicate;
 import org.hibernate.sql.ast.tree.predicate.GroupedPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.InListPredicate;
 import org.hibernate.sql.ast.tree.predicate.InSubQueryPredicate;
 import org.hibernate.sql.ast.tree.predicate.Junction;
@@ -6876,6 +6877,15 @@ public abstract class AbstractSqlAstTranslator<T extends JdbcOperation> implemen
 		appendSql( CLOSE_PARENTHESIS );
 	}
 
+	@Override
+	public void visitInArrayPredicate(InArrayPredicate inArrayPredicate) {
+		sqlBuffer.append( "array_contains(" );
+		inArrayPredicate.getArrayParameter().accept( this );
+		sqlBuffer.append( "," );
+		inArrayPredicate.getTestExpression().accept( this );
+		sqlBuffer.append( ')' );
+	}
+
 	@Override
 	public void visitInSubQueryPredicate(InSubQueryPredicate inSubQueryPredicate) {
 		final SqlTuple lhsTuple;

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/AbstractSqlAstWalker.java

@@ -61,6 +61,7 @@ import org.hibernate.sql.ast.tree.predicate.ComparisonPredicate;
 import org.hibernate.sql.ast.tree.predicate.ExistsPredicate;
 import org.hibernate.sql.ast.tree.predicate.FilterPredicate;
 import org.hibernate.sql.ast.tree.predicate.GroupedPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.InListPredicate;
 import org.hibernate.sql.ast.tree.predicate.InSubQueryPredicate;
 import org.hibernate.sql.ast.tree.predicate.Junction;
@@ -380,6 +381,12 @@ public class AbstractSqlAstWalker implements SqlAstWalker {
 		}
 	}
 
+	@Override
+	public void visitInArrayPredicate(InArrayPredicate predicate) {
+		predicate.getTestExpression().accept( this );
+		predicate.getArrayParameter().accept( this );
+	}
+
 	@Override
 	public void visitInSubQueryPredicate(InSubQueryPredicate inSubQueryPredicate) {
 		inSubQueryPredicate.getTestExpression().accept( this );

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/AggregateFunctionChecker.java

@@ -45,6 +45,7 @@ import org.hibernate.sql.ast.tree.from.ValuesTableReference;
 import org.hibernate.sql.ast.tree.insert.InsertSelectStatement;
 import org.hibernate.sql.ast.tree.predicate.ExistsPredicate;
 import org.hibernate.sql.ast.tree.predicate.FilterPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.InListPredicate;
 import org.hibernate.sql.ast.tree.predicate.InSubQueryPredicate;
 import org.hibernate.sql.ast.tree.select.QueryGroup;
@@ -200,6 +201,10 @@ public class AggregateFunctionChecker extends AbstractSqlAstWalker {
 	public void visitInListPredicate(InListPredicate inListPredicate) {
 	}
 
+	@Override
+	public void visitInArrayPredicate(InArrayPredicate predicate) {
+	}
+
 	@Override
 	public void visitInSubQueryPredicate(InSubQueryPredicate inSubQueryPredicate) {
 	}

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/ExpressionReplacementWalker.java

@@ -59,6 +59,7 @@ import org.hibernate.sql.ast.tree.predicate.ComparisonPredicate;
 import org.hibernate.sql.ast.tree.predicate.ExistsPredicate;
 import org.hibernate.sql.ast.tree.predicate.FilterPredicate;
 import org.hibernate.sql.ast.tree.predicate.GroupedPredicate;
+import org.hibernate.sql.ast.tree.predicate.InArrayPredicate;
 import org.hibernate.sql.ast.tree.predicate.InListPredicate;
 import org.hibernate.sql.ast.tree.predicate.InSubQueryPredicate;
 import org.hibernate.sql.ast.tree.predicate.Junction;
@@ -325,6 +326,12 @@ public class ExpressionReplacementWalker implements SqlAstWalker {
 		}
 	}
 
+	@Override
+	public void visitInArrayPredicate(InArrayPredicate inArrayPredicate) {
+		final Expression replacedTestExpression = replaceExpression( inArrayPredicate.getTestExpression() );
+		returnedNode = new InArrayPredicate( replacedTestExpression, inArrayPredicate.getArrayParameter() );
+	}
+
 	@Override
 	public void visitInSubQueryPredicate(InSubQueryPredicate inSubQueryPredicate) {
 		final Expression testExpression = replaceExpression( inSubQueryPredicate.getTestExpression() );

hibernate-core/src/main/java/org/hibernate/sql/ast/tree/predicate/InArrayPredicate.java

@@ -0,0 +1,43 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.sql.ast.tree.predicate;
+
+import org.hibernate.metamodel.mapping.JdbcMappingContainer;
+import org.hibernate.sql.ast.SqlAstWalker;
+import org.hibernate.sql.ast.tree.expression.Expression;
+import org.hibernate.sql.ast.tree.expression.JdbcParameter;
+
+/**
+ * @author Steve Ebersole
+ */
+public class InArrayPredicate extends AbstractPredicate {
+	private final Expression testExpression;
+	private final JdbcParameter arrayParameter;
+
+	public InArrayPredicate(Expression testExpression, JdbcParameter arrayParameter, JdbcMappingContainer expressionType) {
+		super( expressionType );
+		this.testExpression = testExpression;
+		this.arrayParameter = arrayParameter;
+	}
+
+	public InArrayPredicate(Expression testExpression, JdbcParameter arrayParameter) {
+		this( testExpression, arrayParameter, null );
+	}
+
+	public Expression getTestExpression() {
+		return testExpression;
+	}
+
+	public JdbcParameter getArrayParameter() {
+		return arrayParameter;
+	}
+
+	@Override
+	public void accept(SqlAstWalker sqlTreeWalker) {
+		sqlTreeWalker.visitInArrayPredicate( this );
+	}
+}

hibernate-core/src/main/java/org/hibernate/sql/exec/internal/CallbackImpl.java

@@ -12,7 +12,7 @@ import java.util.List;
 
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.loader.ast.spi.AfterLoadAction;
-import org.hibernate.persister.entity.Loadable;
+import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.sql.exec.spi.Callback;
 
 /**
@@ -32,9 +32,9 @@ public class CallbackImpl implements Callback {
 	}
 
 	@Override
-	public void invokeAfterLoadActions(SharedSessionContractImplementor session, Object entity, Loadable persister) {
+	public void invokeAfterLoadActions(Object entity, EntityMappingType entityMappingType, SharedSessionContractImplementor session) {
 		for ( int i = 0; i < afterLoadActions.size(); i++ ) {
-			afterLoadActions.get( i ).afterLoad( session, entity, persister );
+			afterLoadActions.get( i ).afterLoad( entity, entityMappingType, session );
 		}
 	}
 }

hibernate-core/src/main/java/org/hibernate/sql/exec/internal/CallbackNoOp.java

@@ -8,7 +8,7 @@ package org.hibernate.sql.exec.internal;
 
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.loader.ast.spi.AfterLoadAction;
-import org.hibernate.persister.entity.Loadable;
+import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.sql.exec.spi.Callback;
 
 /**
@@ -26,7 +26,7 @@ public class CallbackNoOp implements Callback {
 	}
 
 	@Override
-	public void invokeAfterLoadActions(SharedSessionContractImplementor session, Object entity, Loadable persister) {
+	public void invokeAfterLoadActions(Object entity, EntityMappingType entityMappingType, SharedSessionContractImplementor session) {
 		// don't do anything
 	}
 }

hibernate-core/src/main/java/org/hibernate/sql/exec/internal/JdbcParameterBindingsImpl.java

@@ -55,7 +55,7 @@ public class JdbcParameterBindingsImpl implements JdbcParameterBindings {
 
 			final Dialect dialect = factory.getJdbcServices().getDialect();
 			final boolean paddingEnabled = factory.getSessionFactoryOptions().inClauseParameterPaddingEnabled();
-			final int inExprLimit = dialect.getInExpressionCountLimit();
+			final int inExprLimit = dialect.getParameterCountLimit();
 
 			for ( ParameterOccurrence occurrence : parameterOccurrences ) {
 				final QueryParameterImplementor<?> param = occurrence.getParameter();

hibernate-core/src/main/java/org/hibernate/sql/exec/spi/Callback.java

@@ -4,12 +4,11 @@
  * License: GNU Lesser General Public License (LGPL), version 2.1 or later
  * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
  */
-
 package org.hibernate.sql.exec.spi;
 
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.loader.ast.spi.AfterLoadAction;
-import org.hibernate.persister.entity.Loadable;
+import org.hibernate.metamodel.mapping.EntityMappingType;
 
 /**
  * Callback to allow SQM interpretation to trigger certain things within ORM.  See the current
@@ -19,7 +18,22 @@ import org.hibernate.persister.entity.Loadable;
  * @author Steve Ebersole
  */
 public interface Callback {
+	/**
+	 * Register a callback action
+	 */
 	void registerAfterLoadAction(AfterLoadAction afterLoadAction);
 
-	void invokeAfterLoadActions(SharedSessionContractImplementor session, Object entity, Loadable persister);
+	/**
+	 * Invoke all {@linkplain #registerAfterLoadAction registered} actions
+	 */
+	void invokeAfterLoadActions(Object entity, EntityMappingType entityMappingType, SharedSessionContractImplementor session);
+
+	/**
+	 * @deprecated Use the {@linkplain #invokeAfterLoadActions(Object, EntityMappingType, SharedSessionContractImplementor) updated signature}
+	 */
+	@SuppressWarnings("removal")
+	@Deprecated(since = "6", forRemoval = true)
+	default void invokeAfterLoadActions(SharedSessionContractImplementor session, Object entity, org.hibernate.persister.entity.Loadable persister) {
+		invokeAfterLoadActions( entity, persister, session );
+	}
 }

hibernate-core/src/main/java/org/hibernate/sql/results/jdbc/internal/DeferredResultSetAccess.java

@@ -107,13 +107,12 @@ public class DeferredResultSetAccess extends AbstractResultSetAccess {
 						lockOptionsToUse.setTimeOut( lockOptions.getTimeOut() );
 						lockOptionsToUse.setScope( lockOptions.getScope() );
 
-						executionContext.getCallback().registerAfterLoadAction(
+						executionContext.getCallback().registerAfterLoadAction( (entity, persister, session) ->
-								(session, entity, persister) ->
+								session.asSessionImplementor().lock(
-									session.asSessionImplementor().lock(
+										persister.getEntityName(),
-											persister.getEntityName(),
+										entity,
-											entity,
+										lockOptionsToUse
-											lockOptionsToUse
+								)
-									)
 						);
 					}
 				}

hibernate-core/src/main/java/org/hibernate/sql/results/jdbc/internal/JdbcValuesSourceProcessingStateStandardImpl.java

@@ -21,19 +21,16 @@ import org.hibernate.event.spi.EventSource;
 import org.hibernate.event.spi.PostLoadEvent;
 import org.hibernate.event.spi.PostLoadEventListener;
 import org.hibernate.event.spi.PreLoadEvent;
-import org.hibernate.persister.entity.Loadable;
-import org.hibernate.sql.exec.spi.Callback;
-import org.hibernate.sql.results.graph.Initializer;
-import org.hibernate.sql.results.graph.collection.internal.ArrayInitializer;
 import org.hibernate.query.spi.QueryOptions;
+import org.hibernate.sql.exec.spi.Callback;
 import org.hibernate.sql.exec.spi.ExecutionContext;
+import org.hibernate.sql.results.graph.Initializer;
 import org.hibernate.sql.results.graph.collection.CollectionInitializer;
+import org.hibernate.sql.results.graph.collection.LoadingCollectionEntry;
+import org.hibernate.sql.results.graph.collection.internal.ArrayInitializer;
+import org.hibernate.sql.results.graph.entity.LoadingEntityEntry;
 import org.hibernate.sql.results.jdbc.spi.JdbcValuesSourceProcessingOptions;
 import org.hibernate.sql.results.jdbc.spi.JdbcValuesSourceProcessingState;
-import org.hibernate.sql.results.graph.collection.LoadingCollectionEntry;
-import org.hibernate.sql.results.graph.entity.LoadingEntityEntry;
-
-import org.jboss.logging.Logger;
 
 /**
  * @author Steve Ebersole
@@ -188,9 +185,9 @@ public class JdbcValuesSourceProcessingStateStandardImpl implements JdbcValuesSo
 					final Callback callback = executionContext.getCallback();
 					if ( callback != null ) {
 						callback.invokeAfterLoadActions(
-								getSession(),
 								loadingEntityEntry.getEntityInstance(),
-								(Loadable) loadingEntityEntry.getDescriptor()
+								loadingEntityEntry.getDescriptor(),
+								getSession()
 						);
 					}
 				}

hibernate-core/src/test/java/org/hibernate/orm/test/batch/BatchAndClassIdAndLazyCollectionTest.java

@@ -9,6 +9,7 @@ import java.util.Set;
 import org.hibernate.Hibernate;
 import org.hibernate.annotations.BatchSize;
 import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.internal.util.StringHelper;
 
 import org.hibernate.testing.TestForIssue;
 import org.hibernate.testing.jdbc.SQLStatementInspector;
@@ -30,6 +31,7 @@ import jakarta.persistence.JoinColumn;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
+import org.assertj.core.api.Assertions;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 import static org.junit.Assert.assertFalse;
@@ -100,14 +102,20 @@ public class BatchAndClassIdAndLazyCollectionTest {
 						c.getParent().getName();
 					}
 					statementInspector.assertExecutedCount( 2 );
-					assertThat( statementInspector.getSqlQueries()
+
-										.get( 0 )
+					if ( scope.getSessionFactory().getJdbcServices().getDialect().supportsStandardArrays() ) {
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 0 ) ).containsOnlyOnce( "?" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "?" );
-					assertThat( statementInspector.getSqlQueries()
+					}
-										.get( 1 )
+					else {
-										.toLowerCase( Locale.ROOT )
+						final int batchSize = scope.getSessionFactory()
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+								.getJdbcServices()
+								.getDialect()
+								.getBatchLoadSizingStrategy()
+								.determineOptimalBatchLoadSize( 1, 5, false );
+						Assertions.assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 0 ), '?' ) ).isEqualTo( batchSize );
+						Assertions.assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 1 ), '?' ) ).isEqualTo( batchSize );
+					}
 				}
 		);
 	}

hibernate-core/src/test/java/org/hibernate/orm/test/batch/BatchAndClassIdTest.java

@@ -29,6 +29,7 @@ import jakarta.persistence.JoinColumn;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
+import org.assertj.core.api.Assertions;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 import static org.junit.Assert.assertFalse;
@@ -94,14 +95,15 @@ public class BatchAndClassIdTest {
 					statementInspector.clear();
 					List<Child> children = session.createQuery( "select c from Child c", Child.class ).getResultList();
 					statementInspector.assertExecutedCount( 3 );
-					assertThat( statementInspector.getSqlQueries()
+					if ( scope.getSessionFactory().getJdbcServices().getDialect().supportsStandardArrays() ) {
-										.get( 1 )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "?" );
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 2 ) ).containsOnlyOnce( "?" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+					}
-					assertThat( statementInspector.getSqlQueries()
+					else {
-										.get( 2 )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 2 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+					}
+
 					statementInspector.clear();
 					for ( Child c : children ) {
 						c.getParent().getName();

hibernate-core/src/test/java/org/hibernate/orm/test/batch/BatchAndEmbeddedIdId2Test.java

@@ -30,6 +30,7 @@ import jakarta.persistence.JoinColumn;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
+import org.assertj.core.api.Assertions;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 import static org.junit.Assert.assertFalse;
@@ -94,14 +95,15 @@ public class BatchAndEmbeddedIdId2Test {
 					statementInspector.clear();
 					List<Child> children = session.createQuery( "select c from Child c", Child.class ).getResultList();
 					statementInspector.assertExecutedCount( 3 );
-					assertThat( statementInspector.getSqlQueries()
+					if ( scope.getSessionFactory().getJdbcServices().getDialect().supportsStandardArrays() ) {
-										.get( 1 )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "?" );
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 2 ) ).containsOnlyOnce( "?" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+					}
-					assertThat( statementInspector.getSqlQueries()
+					else {
-										.get( 2 )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 2 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+					}
+
 					statementInspector.clear();
 					for ( Child c : children ) {
 						c.getParent().getName();

hibernate-core/src/test/java/org/hibernate/orm/test/batch/BatchAndEmbeddedIdIdAndLazyCollectionTest.java

@@ -32,6 +32,7 @@ import jakarta.persistence.JoinColumn;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
+import org.assertj.core.api.Assertions;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 import static org.junit.Assert.assertFalse;
@@ -101,14 +102,15 @@ public class BatchAndEmbeddedIdIdAndLazyCollectionTest {
 						c.getParent().getName();
 					}
 					statementInspector.assertExecutedCount( 2 );
-					assertThat( statementInspector.getSqlQueries()
+
-										.get( 0 )
+					if ( scope.getSessionFactory().getJdbcServices().getDialect().supportsStandardArrays() ) {
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 0 ) ).containsOnlyOnce( "?" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "?" );
-					assertThat( statementInspector.getSqlQueries()
+					}
-										.get( 1 )
+					else {
-										.toLowerCase( Locale.ROOT )
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 0 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+						Assertions.assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
+					}
 				}
 		);
 	}

hibernate-core/src/test/java/org/hibernate/orm/test/batch/BatchAndEmbeddedIdIdTest.java

@@ -31,7 +31,7 @@ import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
 
-import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
@@ -89,26 +89,25 @@ public class BatchAndEmbeddedIdIdTest {
 	@Test
 	public void testSelectChild(SessionFactoryScope scope) {
 		SQLStatementInspector statementInspector = (SQLStatementInspector) scope.getStatementInspector();
-		scope.inTransaction(
+		scope.inTransaction( (session) -> {
-				session -> {
+			statementInspector.clear();
-					statementInspector.clear();
+			List<Child> children = session.createQuery( "select c from Child c", Child.class ).getResultList();
-					List<Child> children = session.createQuery( "select c from Child c", Child.class ).getResultList();
+			statementInspector.assertExecutedCount( 3 );
-					statementInspector.assertExecutedCount( 3 );
+			if ( scope.getSessionFactory().getJdbcServices().getDialect().supportsStandardArrays() ) {
-					assertThat( statementInspector.getSqlQueries()
+				assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "?" );
-										.get( 1 )
+				assertThat( statementInspector.getSqlQueries().get( 2 ) ).containsOnlyOnce( "?" );
-										.toLowerCase( Locale.ROOT )
+			}
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+			else {
-					assertThat( statementInspector.getSqlQueries()
+				assertThat( statementInspector.getSqlQueries().get( 1 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.get( 2 )
+				assertThat( statementInspector.getSqlQueries().get( 2 ) ).containsOnlyOnce( "in(?,?,?,?,?)" );
-										.toLowerCase( Locale.ROOT )
+			}
-										.contains( "in(?,?,?,?,?)" ) ).isTrue();
+
-					statementInspector.clear();
+			statementInspector.clear();
-					for ( Child c : children ) {
+			for ( Child c : children ) {
-						c.getParent().getName();
+				c.getParent().getName();
-					}
+			}
-					statementInspector.assertExecutedCount( 0 );
+			statementInspector.assertExecutedCount( 0 );
-				}
+		} );
-		);
 	}
 
 	@Test

hibernate-core/src/test/java/org/hibernate/orm/test/batch/MultiKeyLoadSizingStrategyTests.java

@@ -0,0 +1,38 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.orm.test.batch;
+
+import org.hibernate.engine.jdbc.spi.JdbcServices;
+import org.hibernate.loader.ast.spi.MultiKeyLoadSizingStrategy;
+
+import org.hibernate.testing.orm.junit.ServiceRegistry;
+import org.hibernate.testing.orm.junit.ServiceRegistryScope;
+
+import org.junit.jupiter.api.Test;
+
+import static java.util.Locale.ROOT;
+
+/**
+ * @author Steve Ebersole
+ */
+@ServiceRegistry
+public class MultiKeyLoadSizingStrategyTests {
+	@Test
+	public void testSizes(ServiceRegistryScope scope) {
+		scope.withService( JdbcServices.class, (jdbcServices) -> {
+			final MultiKeyLoadSizingStrategy sizingStrategy = jdbcServices.getDialect().getBatchLoadSizingStrategy();
+
+			check( 1, 1000, true, sizingStrategy );
+			check( 1, 1000, false, sizingStrategy );
+		} );
+	}
+
+	private void check(int columns, int size, boolean pad, MultiKeyLoadSizingStrategy sizingStrategy) {
+		final int value = sizingStrategy.determineOptimalBatchLoadSize( columns, size, pad );
+		System.out.printf( ROOT, "(%s, %s, %s) - %s%n", columns, size, pad, value );
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/batchfetch/A.java

@@ -8,14 +8,12 @@ package org.hibernate.orm.test.batchfetch;
 
 import jakarta.persistence.Entity;
 import jakarta.persistence.FetchType;
-import jakarta.persistence.GeneratedValue;
 import jakarta.persistence.Id;
 import jakarta.persistence.OneToOne;
 
 @Entity
 public class A {
   @Id
-  @GeneratedValue
   private Integer id;
 
   private String otherProperty;
@@ -23,6 +21,13 @@ public class A {
   @OneToOne(fetch = FetchType.LAZY)
   private B b;
 
+  public A() {
+  }
+
+  public A(Integer id) {
+    this.id = id;
+  }
+
   public Integer getId() {
     return id;
   }

hibernate-core/src/test/java/org/hibernate/orm/test/batchfetch/B.java

@@ -25,6 +25,14 @@ public class B {
 
   private String otherProperty;
 
+  public B() {
+  }
+
+  public B(Integer idPart1, Integer idPart2) {
+    this.idPart1 = idPart1;
+    this.idPart2 = idPart2;
+  }
+
   public Integer getIdPart1() {
     return idPart1;
   }

hibernate-core/src/test/java/org/hibernate/orm/test/batchfetch/BId.java

@@ -15,6 +15,14 @@ public class BId
   private Integer idPart1;
   private Integer idPart2;
 
+  public BId() {
+  }
+
+  public BId(Integer idPart1, Integer idPart2) {
+    this.idPart1 = idPart1;
+    this.idPart2 = idPart2;
+  }
+
   public Integer getIdPart1() {
     return idPart1;
   }
@@ -35,4 +43,4 @@ public class BId
   public String toString() {
     return "BId (" + idPart1 + ", " + idPart2 + ")";
   }
-}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/batchfetch/BatchFetchStrategyLoadingTests.java

@@ -0,0 +1,166 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html.
+ */
+package org.hibernate.orm.test.batchfetch;
+
+import org.hibernate.Hibernate;
+import org.hibernate.annotations.BatchSize;
+import org.hibernate.internal.util.StringHelper;
+import org.hibernate.loader.ast.internal.MultiKeyLoadHelper;
+
+import org.hibernate.testing.jdbc.SQLStatementInspector;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import jakarta.persistence.Basic;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Steve Ebersole
+ */
+public class BatchFetchStrategyLoadingTests {
+	@Test
+	@DomainModel( annotatedClasses = {
+			BatchFetchStrategyLoadingTests.Thing1.class,
+			BatchFetchStrategyLoadingTests.Thing2.class
+	})
+	@SessionFactory( useCollectingStatementInspector = true )
+	public void testIt(SessionFactoryScope scope) {
+		final SQLStatementInspector statementInspector = scope.getCollectingStatementInspector();
+		statementInspector.clear();
+
+		scope.inTransaction( (session) -> {
+			final Thing2 thing21 = session.getReference( Thing2.class, 1 );
+			final Thing2 thing22 = session.getReference( Thing2.class, 2 );
+			final Thing2 thing23 = session.getReference( Thing2.class, 3 );
+
+			assertThat( statementInspector.getSqlQueries() ).isEmpty();
+			assertThat( Hibernate.isInitialized( thing21 ) ).isFalse();
+			assertThat( Hibernate.isInitialized( thing22 ) ).isFalse();
+			assertThat( Hibernate.isInitialized( thing23 ) ).isFalse();
+
+			final String name = thing21.getName();
+			assertThat( name ).isEqualTo( "thing-2.1" );
+
+			assertThat( statementInspector.getSqlQueries() ).hasSize( 1 );
+			if ( MultiKeyLoadHelper.supportsSqlArrayType( scope.getSessionFactory().getJdbcServices().getDialect() ) ) {
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 0 ), "?" ) ).isEqualTo( 1 );
+			}
+			else {
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 0 ), "?" ) ).isEqualTo( 64 );
+			}
+			assertThat( Hibernate.isInitialized( thing21 ) ).isTrue();
+			assertThat( Hibernate.isInitialized( thing22 ) ).isTrue();
+			assertThat( Hibernate.isInitialized( thing23 ) ).isTrue();
+		} );
+	}
+
+	@BeforeEach
+	public void createTestData(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			final Thing2 thing2 = new Thing2( 1, "thing-2.1" );
+			final Thing1 thing1 = new Thing1( 1, "thing-1", thing2 );
+
+			session.persist( thing2 );
+			session.persist( thing1 );
+
+			session.persist( new Thing2( 2, "thing-2.2" ) );
+			session.persist( new Thing2( 3, "thing-2.3" ) );
+		} );
+	}
+
+	@AfterEach
+	public void dropTestData(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			session.createMutationQuery( "delete Thing1" ).executeUpdate();
+			session.createMutationQuery( "delete Thing2" ).executeUpdate();
+		} );
+	}
+
+	@Entity( name = "Thing1" )
+	@Table( name = "Thing1" )
+	public static class Thing1 {
+	    @Id
+	    private Integer id;
+	    @Basic
+		private String name;
+		@ManyToOne
+		@JoinColumn( name = "thing2_fk" )
+		private Thing2 thing2;
+
+		protected Thing1() {
+			// for use by Hibernate
+		}
+
+		public Thing1(Integer id, String name, Thing2 thing2) {
+			this.id = id;
+			this.name = name;
+			this.thing2 = thing2;
+		}
+
+		public Integer getId() {
+			return id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public Thing2 getThing2() {
+			return thing2;
+		}
+
+		public void setThing2(Thing2 thing2) {
+			this.thing2 = thing2;
+		}
+	}
+
+	@Entity( name = "Thing2" )
+	@Table( name = "Thing2" )
+	@BatchSize( size = 64 )
+	public static class Thing2 {
+	    @Id
+	    private Integer id;
+	    @Basic
+		private String name;
+
+		protected Thing2() {
+			// for use by Hibernate
+		}
+
+		public Thing2(Integer id, String name) {
+			this.id = id;
+			this.name = name;
+		}
+
+		public Integer getId() {
+			return id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/batchfetch/DynamicBatchFetchTest.java

@@ -9,15 +9,19 @@ package org.hibernate.orm.test.batchfetch;
 import java.util.List;
 
 import org.hibernate.Hibernate;
+import org.hibernate.annotations.BatchSize;
 import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.internal.util.collections.CollectionHelper;
 
 import org.hibernate.testing.orm.junit.DomainModel;
 import org.hibernate.testing.orm.junit.ServiceRegistry;
 import org.hibernate.testing.orm.junit.SessionFactory;
 import org.hibernate.testing.orm.junit.SessionFactoryScope;
 import org.hibernate.testing.orm.junit.Setting;
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -34,6 +38,8 @@ public class DynamicBatchFetchTest {
 
 	@Test
 	public void testDynamicBatchFetch(SessionFactoryScope scope) {
+		currentId = 1;
+
 		Integer aId1 = createAAndB( "foo_1", scope );
 		Integer aId2 = createAAndB( "foo_2", scope );
 
@@ -41,6 +47,7 @@ public class DynamicBatchFetchTest {
 				session -> {
 					List resultList = session.createQuery( "from A where id in (" + aId1 + "," + aId2 + ") order by id" )
 							.list();
+					assertThat( resultList ).isNotEmpty();
 					A a1 = (A) resultList.get( 0 );
 					A a2 = (A) resultList.get( 1 );
 					assertEquals( aId1, a1.getId() );
@@ -60,17 +67,14 @@ public class DynamicBatchFetchTest {
 	private int createAAndB(String otherProperty, SessionFactoryScope scope) {
 		scope.inTransaction(
 				session -> {
-					B b = new B();
+					B b = new B( currentId, currentId );
-					b.setIdPart1( currentId );
-					b.setIdPart2( currentId );
 					b.setOtherProperty( otherProperty );
-					session.save( b );
+					session.persist( b );
 
-					A a = new A();
+					A a = new A( currentId );
-					a.setId( currentId );
 					a.setB( b );
 
-					session.save( a );
+					session.persist( a );
 				}
 		);
 
@@ -78,4 +82,41 @@ public class DynamicBatchFetchTest {
 
 		return currentId - 1;
 	}
+
+	/**
+	 * Tests the handling of multi-loads with regard to BatchLoadSizingStrategy and correlation
+	 * to batch fetching.  Show that both suffer from the previous behavior of always using the
+	 * mapped {@link BatchSize#size()} which leads to predicates with too many parameters with
+	 * large batch-sizes
+	 */
+	@Test
+	public void testMultiLoad(SessionFactoryScope scope) {
+		final List<BId> bIdList = CollectionHelper.arrayList( 2000 );
+		scope.inTransaction( (session) -> {
+			for ( int i = 0; i < 2000; i++ ) {
+				bIdList.add( new BId( i, i ) );
+				final B b = new B( i, i );
+				session.persist( b );
+
+				A a = new A( i );
+				a.setB( b );
+
+				session.persist( b );
+				session.persist( a );
+			}
+		} );
+
+		scope.inTransaction( (session) -> {
+			final List<B> list = session.byMultipleIds( B.class ).multiLoad( bIdList );
+			assertThat( list ).isNotEmpty();
+		} );
+	}
+
+	@AfterEach
+	public void dropTestData(SessionFactoryScope scope) {
+		scope.inTransaction( (session) -> {
+			session.createQuery( "delete A" ).executeUpdate();
+			session.createQuery( "delete B" ).executeUpdate();
+		} );
+	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/batchfetch/NestedLazyManyToOneTest.java

@@ -10,6 +10,8 @@ import java.util.HashSet;
 import java.util.Set;
 
 import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.internal.util.StringHelper;
+import org.hibernate.loader.ast.internal.MultiKeyLoadHelper;
 
 import org.hibernate.testing.jdbc.SQLStatementInspector;
 import org.hibernate.testing.orm.junit.DomainModel;
@@ -30,6 +32,7 @@ import jakarta.persistence.OrderBy;
 
 import static jakarta.persistence.CascadeType.ALL;
 import static jakarta.persistence.FetchType.LAZY;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 /**
@@ -111,18 +114,24 @@ public class NestedLazyManyToOneTest {
 				else {
 					Set<Entity3> children3 = child2.getChildren();
 					if ( child2.getId().equals( "0_0" ) ) {
-						assertEquals( 5, children3.size() );
+						assertEquals( 5, children3.size(), "Size of `Child2(0_0).children3` did not match expectation" );
 					}
 					else {
-						assertEquals( 0, children3.size() );
+						assertEquals( 0, children3.size(), "Size of `Child2(" + child2.getId() + ").children3` did not match expectation" );
 					}
 				}
 			}
 
 			assertEquals( 8, entity1.getChildren().size() );
-			statementInspector.assertExecutedCount( 3 ); // 1 for Entity1, 1 for Entity2, 1 for Entity3
+			// 1 for Entity1, 1 for Entity2, 1 for Entity3
+			statementInspector.assertExecutedCount( 3 );
 			statementInspector.assertNumberOfOccurrenceInQueryNoSpace( 1, QUESTION_MARK, 1 );
-			statementInspector.assertNumberOfOccurrenceInQueryNoSpace( 2, QUESTION_MARK, 5 );
+			if ( MultiKeyLoadHelper.supportsSqlArrayType( scope.getSessionFactory().getJdbcServices().getDialect() ) ) {
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 2 ), '?' ) ).isEqualTo( 1 );
+			}
+			else {
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 2 ), '?' ) ).isEqualTo( 5 );
+			}
 		} );
 	}
 
@@ -143,11 +152,18 @@ public class NestedLazyManyToOneTest {
 				}
 			}
 
-			assertEquals( 8, entity1.getChildren().size() );
+			assertThat( entity1.getChildren() ).hasSize( 8 );
-			statementInspector.assertExecutedCount( 4 ); // 1 for Entity1, 1 for Entity2, 2 for Entity3
+			// 1 for Entity1, 1 for Entity2, 2 for Entity3
-			statementInspector.assertNumberOfOccurrenceInQueryNoSpace( 1, QUESTION_MARK, 1 );
+			assertThat( statementInspector.getSqlQueries() ).hasSize( 4 );
-			statementInspector.assertNumberOfOccurrenceInQueryNoSpace( 2, QUESTION_MARK, 5 );
+			assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 1 ), '?' ) ).isEqualTo( 1 );
-			statementInspector.assertNumberOfOccurrenceInQueryNoSpace( 3, QUESTION_MARK, 3 );
+			if ( MultiKeyLoadHelper.supportsSqlArrayType( scope.getSessionFactory().getJdbcServices().getDialect() ) ) {
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 2 ), '?' ) ).isEqualTo( 1 );
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 3 ), '?' ) ).isEqualTo( 1 );
+			}
+			else {
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 2 ), '?' ) ).isEqualTo( 5 );
+				assertThat( StringHelper.count( statementInspector.getSqlQueries().get( 3 ), '?' ) ).isEqualTo( 5 );
+			}
 		} );
 	}
 

hibernate-core/src/test/java/org/hibernate/orm/test/id/usertype/UserTypeComparableIdTest.java

@@ -17,6 +17,7 @@ import org.hibernate.HibernateException;
 import org.hibernate.annotations.Type;
 import org.hibernate.cfg.AvailableSettings;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.usertype.EnhancedUserType;
 import org.hibernate.usertype.UserType;
 
 import org.hibernate.testing.TestForIssue;
@@ -122,7 +123,7 @@ public class UserTypeComparableIdTest {
 		}
 	}
 
-	public static class CustomIdType implements UserType<CustomId>, Comparator<CustomId> {
+	public static class CustomIdType implements EnhancedUserType<CustomId>, Comparator<CustomId> {
 
 		@Override
 		public int getSqlType() {
@@ -195,5 +196,34 @@ public class UserTypeComparableIdTest {
 		public CustomId replace(CustomId original, CustomId target, Object owner) throws HibernateException {
 			return original;
 		}
+
+		@Override
+		public String toSqlLiteral(CustomId value) {
+			return toString( value );
+		}
+
+		@Override
+		public String toString(CustomId customId) throws HibernateException {
+			if ( customId == null ) {
+				return null;
+			}
+
+			final Long longValue = customId.getValue();
+			if ( longValue == null ) {
+				return null;
+			}
+
+			return longValue.toString();
+		}
+
+		@Override
+		public CustomId fromStringValue(CharSequence sequence) throws HibernateException {
+			if ( sequence == null ) {
+				return null;
+			}
+
+			final long longValue = Long.parseLong( sequence.toString() );
+			return new CustomId( longValue );
+		}
 	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/id/usertype/UserTypeNonComparableIdTest.java

@@ -20,6 +20,7 @@ import jakarta.persistence.Table;
 import org.hibernate.HibernateException;
 import org.hibernate.annotations.Type;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.usertype.EnhancedUserType;
 import org.hibernate.usertype.UserType;
 
 import org.hibernate.testing.TestForIssue;
@@ -109,7 +110,7 @@ public class UserTypeNonComparableIdTest {
 		}
 	}
 
-	public static class CustomIdType implements UserType<CustomId> {
+	public static class CustomIdType implements EnhancedUserType<CustomId> {
 
 		@Override
 		public int getSqlType() {
@@ -177,5 +178,34 @@ public class UserTypeNonComparableIdTest {
 		public CustomId replace(CustomId original, CustomId target, Object owner) throws HibernateException {
 			return original;
 		}
+
+		@Override
+		public String toSqlLiteral(CustomId customId) {
+			return toString( customId );
+		}
+
+		@Override
+		public String toString(CustomId customId) throws HibernateException {
+			if ( customId == null ) {
+				return null;
+			}
+
+			final Long longValue = customId.getValue();
+			if ( longValue == null ) {
+				return null;
+			}
+
+			return longValue.toString();
+		}
+
+		@Override
+		public CustomId fromStringValue(CharSequence sequence) throws HibernateException {
+			if ( sequence == null ) {
+				return null;
+			}
+
+			final long longValue = Long.parseLong( sequence.toString() );
+			return new CustomId( longValue );
+		}
 	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/loading/LoadingSmokeTests.java

@@ -60,7 +60,7 @@ public class LoadingSmokeTests {
 							.getRuntimeMetamodels().getMappingMetamodel()
 							.getEntityDescriptor( BasicEntity.class );
 
-					final SingleIdEntityLoader singleIdEntityLoader = entityDescriptor.getSingleIdEntityLoader();
+					final SingleIdEntityLoader singleIdEntityLoader = entityDescriptor.getSingleIdLoader();
 					assertThat( singleIdEntityLoader, instanceOf( SingleIdEntityLoaderStandardImpl.class ) );
 					assertThat(
 							( (SingleIdEntityLoaderStandardImpl) singleIdEntityLoader ).getNonReusablePlansGenerated().get(),

hibernate-core/src/test/java/org/hibernate/orm/test/loading/multiLoad/MultiLoadSubSelectCollectionDialectWithLimitTest.java

@@ -10,10 +10,13 @@ import org.hibernate.annotations.Fetch;
 import org.hibernate.annotations.FetchMode;
 import org.hibernate.cfg.AvailableSettings;
 import org.hibernate.dialect.DatabaseVersion;
+import org.hibernate.dialect.Dialect;
 import org.hibernate.dialect.H2Dialect;
 import org.hibernate.engine.jdbc.dialect.spi.DialectResolutionInfo;
+import org.hibernate.loader.ast.internal.MultiKeyLoadHelper;
 
 import org.hibernate.testing.TestForIssue;
+import org.hibernate.testing.jdbc.SQLStatementInspector;
 import org.hibernate.testing.orm.junit.DomainModel;
 import org.hibernate.testing.orm.junit.RequiresDialect;
 import org.hibernate.testing.orm.junit.ServiceRegistry;
@@ -34,6 +37,7 @@ import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
 
 import static jakarta.persistence.GenerationType.AUTO;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -45,7 +49,7 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
 @ServiceRegistry(
 		settingProviders = @SettingProvider( provider = MultiLoadSubSelectCollectionDialectWithLimitTest.TestSettingProvider.class, settingName = AvailableSettings.DIALECT)
 )
-@SessionFactory(generateStatistics = true)
+@SessionFactory(generateStatistics = true, useCollectingStatementInspector = true)
 @RequiresDialect( H2Dialect.class )
 public class MultiLoadSubSelectCollectionDialectWithLimitTest {
 
@@ -104,37 +108,52 @@ public class MultiLoadSubSelectCollectionDialectWithLimitTest {
 	@Test
 	@TestForIssue(jiraKey = "HHH-12740")
 	public void testSubselect(SessionFactoryScope scope) {
+		final SQLStatementInspector statementInspector = scope.getCollectingStatementInspector();
+		statementInspector.clear();
+
 		scope.inTransaction(
 				session -> {
 					List<Parent> list = session.byMultipleIds( Parent.class ).multiLoad( ids( 56 ) );
 					assertEquals( 56, list.size() );
 
 					// None of the collections should be loaded yet
+					assertThat( statementInspector.getSqlQueries() ).hasSize( 1 );
 					for ( Parent p : list ) {
 						assertFalse( Hibernate.isInitialized( p.children ) );
 					}
 
-					// When the first collection is loaded, the full batch of 50 collections
+					statementInspector.clear();
-					// should be loaded.
+
+					// When the first collection is loaded multiple will be initialized
 					Hibernate.initialize( list.get( 0 ).children );
 
-					for ( int i = 0; i < 50; i++ ) {
+					// exactly how depends on whether the Dialect supports use of SQL ARRAY
-						assertTrue( Hibernate.isInitialized( list.get( i ).children ) );
+					final Dialect dialect = scope.getSessionFactory().getFastSessionServices().jdbcServices.getDialect();
-						assertEquals( i + 1, list.get( i ).children.size() );
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( Hibernate.isInitialized( list.get( 0 ).children ) ).isTrue();
+						assertThat( Hibernate.isInitialized( list.get( 50 ).children ) ).isTrue();
+						assertThat( Hibernate.isInitialized( list.get( 52 ).children ) ).isTrue();
+						assertThat( statementInspector.getSqlQueries() ).hasSize( 1 );
 					}
+					else {
+						for ( int i = 0; i < 50; i++ ) {
+							assertTrue( Hibernate.isInitialized( list.get( i ).children ) );
+							assertEquals( i + 1, list.get( i ).children.size() );
+						}
 
-					// The collections for the 51st through 56th entities should still be uninitialized
+						// The collections for the 51st through 56th entities should still be uninitialized
-					for ( int i = 50; i < 56; i++ ) {
+						for ( int i = 50; i < 56; i++ ) {
-						assertFalse( Hibernate.isInitialized( list.get( i ).children ) );
+							assertFalse( Hibernate.isInitialized( list.get( i ).children ) );
-					}
+						}
 
-					// When the 51st collection gets initialized, the remaining collections should
+						// When the 51st collection gets initialized, the remaining collections should
-					// also be initialized.
+						// also be initialized.
-					Hibernate.initialize( list.get( 50 ).children );
+						Hibernate.initialize( list.get( 50 ).children );
 
-					for ( int i = 50; i < 56; i++ ) {
+						for ( int i = 50; i < 56; i++ ) {
-						assertTrue( Hibernate.isInitialized( list.get( i ).children ) );
+							assertTrue( Hibernate.isInitialized( list.get( i ).children ) );
-						assertEquals( i + 1, list.get( i ).children.size() );
+							assertEquals( i + 1, list.get( i ).children.size() );
+						}
 					}
 				}
 		);

hibernate-core/src/test/java/org/hibernate/orm/test/loading/multiLoad/MultiLoadTest.java

@@ -14,11 +14,11 @@ import org.hibernate.Hibernate;
 import org.hibernate.annotations.BatchSize;
 import org.hibernate.cache.spi.access.AccessType;
 import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.dialect.Dialect;
 import org.hibernate.engine.spi.EntityEntry;
 import org.hibernate.engine.spi.EntityKey;
-import org.hibernate.engine.spi.SharedSessionContractImplementor;
-import org.hibernate.engine.spi.Status;
 import org.hibernate.internal.util.StringHelper;
+import org.hibernate.loader.ast.internal.MultiKeyLoadHelper;
 import org.hibernate.stat.Statistics;
 
 import org.hibernate.testing.TestForIssue;
@@ -100,7 +100,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 5 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 5 ) );
+					}
 				}
 		);
 	}
@@ -314,7 +324,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 2 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 2 ) );
+					}
 				}
 		);
 	}
@@ -369,7 +389,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 2 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 2 ) );
+					}
 				}
 		);
 	}
@@ -400,7 +430,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 2 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 2 ) );
+					}
 				}
 		);
 	}
@@ -437,7 +477,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 2 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 2 ) );
+					}
 				} );
 	}
 
@@ -467,7 +517,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 2 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 2 ) );
+					}
 				} );
 	}
 
@@ -503,7 +563,17 @@ public class MultiLoadTest {
 							statementInspector.getSqlQueries().get( 0 ),
 							'?'
 					);
-					assertThat( paramCount, is( 2 ) );
+
+					final Dialect dialect = session.getSessionFactory()
+							.getFastSessionServices()
+							.jdbcServices
+							.getDialect();
+					if ( MultiKeyLoadHelper.supportsSqlArrayType( dialect ) ) {
+						assertThat( paramCount, is( 1 ) );
+					}
+					else {
+						assertThat( paramCount, is( 2 ) );
+					}
 				} );
 	}
 

hibernate-core/src/test/java/org/hibernate/orm/test/query/sqm/BaseSqmUnitTest.java

@@ -11,6 +11,7 @@ import org.hibernate.cfg.AvailableSettings;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.loader.ast.spi.AfterLoadAction;
+import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.metamodel.spi.MappingMetamodelImplementor;
 import org.hibernate.persister.entity.Loadable;
 import org.hibernate.query.sqm.tree.select.SqmSelectStatement;
@@ -51,7 +52,7 @@ public abstract class BaseSqmUnitTest
 	}
 
 	@Override
-	public void invokeAfterLoadActions(SharedSessionContractImplementor session, Object entity, Loadable persister) {
+	public void invokeAfterLoadActions(Object entity, EntityMappingType entityMappingType, SharedSessionContractImplementor session) {
 	}
 
 	protected SqmSelectStatement<?> interpretSelect(String hql) {