HHH-18375 Reuse previous row state when result cardinality is duplicated

hibernate-core/src/main/java/org/hibernate/sql/results/graph/AssemblerCreationState.java

@@ -21,6 +21,10 @@ public interface AssemblerCreationState {
 		return false;
 	}
 
+	default boolean containsMultipleCollectionFetches() {
+		return true;
+	}
+
 	int acquireInitializerId();
 
 	Initializer<?> resolveInitializer(

hibernate-core/src/main/java/org/hibernate/sql/results/graph/FetchList.java

@@ -79,4 +79,20 @@ public interface FetchList extends Iterable<Fetch> {
 		return false;
 	}
 
+	default int getCollectionFetchesCount() {
+		int collectionFetchesCount = 0;
+		for ( Fetch fetch : this ) {
+			if ( fetch instanceof EagerCollectionFetch ) {
+				collectionFetchesCount++;
+			}
+			else {
+				final FetchParent fetchParent = fetch.asFetchParent();
+				if ( fetchParent != null ) {
+					collectionFetchesCount += fetchParent.getCollectionFetchesCount();
+				}
+			}
+		}
+		return collectionFetchesCount;
+	}
+
 }

hibernate-core/src/main/java/org/hibernate/sql/results/graph/FetchParent.java

@@ -95,6 +95,10 @@ public interface FetchParent extends DomainResultGraphNode {
 
 	boolean containsCollectionFetches();
 
+	default int getCollectionFetchesCount() {
+		return getFetches().getCollectionFetchesCount();
+	}
+
 	@Override
 	default void collectValueIndexesToCache(BitSet valueIndexes) {
 		for ( Fetch fetch : getFetches() ) {

hibernate-core/src/main/java/org/hibernate/sql/results/graph/Initializer.java

@@ -86,7 +86,7 @@ public interface Initializer<Data extends InitializerData> {
 		// by default - nothing to do
 
 	/**
-	 * Step 1 - Resolve the key value for this initializer for the current
+	 * Step 1.1 - Resolve the key value for this initializer for the current
 	 * row and then recurse to the sub-initializers.
 	 *
 	 * After this point, the initializer knows whether further processing is necessary
@@ -98,6 +98,20 @@ public interface Initializer<Data extends InitializerData> {
 		resolveKey( getData( rowProcessingState ) );
 	}
 
+	/**
+	 * Step 1.2 - Special variant of {@link #resolveKey(InitializerData)} that allows the reuse of key value
+	 * and instance value from the previous row.
+	 *
+	 * @implSpec Defaults to simply delegating to {@link #resolveKey(InitializerData)}.
+	 */
+	default void resolveFromPreviousRow(Data data) {
+		resolveKey( data );
+	}
+
+	default void resolveFromPreviousRow(RowProcessingState rowProcessingState) {
+		resolveFromPreviousRow( getData( rowProcessingState ) );
+	}
+
 	/**
 	 * Step 2.1 - Using the key resolved in {@link #resolveKey}, resolve the
 	 * instance (of the thing initialized) to use for the current row.

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/LoadingCollectionEntry.java

@@ -7,6 +7,7 @@
 package org.hibernate.sql.results.graph.collection;
 
 import java.util.List;
+import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
 import org.hibernate.collection.spi.PersistentCollection;
@@ -44,6 +45,13 @@ public interface LoadingCollectionEntry {
 	 */
 	void load(Consumer<List<Object>> loadingEntryConsumer);
 
+	/**
+	 * Callback for row loading.  Allows delayed List creation
+	 */
+	default <T> void load(T arg1, BiConsumer<T, List<Object>> loadingEntryConsumer) {
+		load( list -> loadingEntryConsumer.accept( arg1, list ) );
+	}
+
 	/**
 	 * Complete the load
 	 */

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/AbstractCollectionInitializer.java

@@ -117,6 +117,24 @@ public abstract class AbstractCollectionInitializer<Data extends AbstractCollect
 		}
 	}
 
+	@Override
+	public void resolveFromPreviousRow(Data data) {
+		if ( data.getState() == State.UNINITIALIZED ) {
+			if ( data.collectionKey == null ) {
+				setMissing( data );
+			}
+			else {
+				if ( collectionKeyResultAssembler != null ) {
+					final Initializer<?> initializer = collectionKeyResultAssembler.getInitializer();
+					if ( initializer != null ) {
+						initializer.resolveFromPreviousRow( data.getRowProcessingState() );
+					}
+				}
+				data.setState( State.RESOLVED );
+			}
+		}
+	}
+
 	protected void setMissing(Data data) {
 		data.setState( State.MISSING );
 		data.collectionKey = null;

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/AbstractImmediateCollectionInitializer.java

@@ -12,7 +12,6 @@ import java.util.function.BiConsumer;
 import org.hibernate.LockMode;
 import org.hibernate.collection.spi.CollectionSemantics;
 import org.hibernate.collection.spi.PersistentCollection;
-import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.engine.spi.PersistenceContext;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.internal.log.LoggingHelper;
@@ -27,7 +26,6 @@ import org.hibernate.sql.results.graph.Initializer;
 import org.hibernate.sql.results.graph.InitializerData;
 import org.hibernate.sql.results.graph.InitializerParent;
 import org.hibernate.sql.results.graph.collection.LoadingCollectionEntry;
-import org.hibernate.sql.results.graph.entity.internal.EntityInitializerImpl;
 import org.hibernate.sql.results.internal.LoadingCollectionEntryImpl;
 import org.hibernate.sql.results.jdbc.spi.RowProcessingState;
 
@@ -42,12 +40,12 @@ import org.checkerframework.checker.nullness.qual.Nullable;
  * @implNote Mainly an intention contract wrt the immediacy of the fetch.
  */
 public abstract class AbstractImmediateCollectionInitializer<Data extends AbstractImmediateCollectionInitializer.ImmediateCollectionInitializerData>
-		extends AbstractCollectionInitializer<Data> {
+		extends AbstractCollectionInitializer<Data> implements BiConsumer<Data, List<Object>> {
 
 	/**
 	 * refers to the rows entry in the collection.  null indicates that the collection is empty
 	 */
-	private final @Nullable DomainResultAssembler<?> collectionValueKeyResultAssembler;
+	protected final @Nullable DomainResultAssembler<?> collectionValueKeyResultAssembler;
 
 	public static class ImmediateCollectionInitializerData extends CollectionInitializerData {
 
@@ -137,6 +135,14 @@ public abstract class AbstractImmediateCollectionInitializer<Data extends Abstra
 		}
 	}
 
+	@Override
+	public void resolveFromPreviousRow(Data data) {
+		super.resolveFromPreviousRow( data );
+		if ( data.getState() == State.RESOLVED ) {
+			resolveKeySubInitializers( data );
+		}
+	}
+
 	/**
 	 * Returns whether the collection value key is missing.
 	 */
@@ -185,7 +191,12 @@ public abstract class AbstractImmediateCollectionInitializer<Data extends Abstra
 			return;
 		}
 
-		resolveCollectionKey( data, true );
+		// Being a result initializer means that this collection initializer is for lazy loading,
+		// which has a very high chance that a collection resolved of the previous row is the same for the current row,
+		// so pass that flag as indicator whether to check previous row state.
+		// Note that we don't need to check previous rows in other cases,
+		// because the previous row checks are done by the owner of the collection initializer already.
+		resolveCollectionKey( data, isResultInitializer );
 		if ( data.getState() != State.KEY_RESOLVED ) {
 			return;
 		}
@@ -429,20 +440,17 @@ public abstract class AbstractImmediateCollectionInitializer<Data extends Abstra
 		}
 		data.setState( State.INITIALIZED );
 
-		final RowProcessingState initializerRowProcessingState = data.getRowProcessingState();
 		if ( data.collectionValueKey == null && collectionValueKeyResultAssembler != null ) {
 			final Initializer<?> initializer = collectionValueKeyResultAssembler.getInitializer();
 			if ( initializer != null ) {
-				data.collectionValueKey = collectionValueKeyResultAssembler.assemble( initializerRowProcessingState );
+				data.collectionValueKey = collectionValueKeyResultAssembler.assemble( data.getRowProcessingState() );
 			}
 		}
 
 		// the RHS key value of the association - determines if the row contains an element of the initializing collection
 		if ( collectionValueKeyResultAssembler == null || data.collectionValueKey != null ) {
 			// the row contains an element in the collection...
-			data.responsibility.load(
-					loadingState -> readCollectionRow( data.collectionKey, loadingState, initializerRowProcessingState )
-			);
+			data.responsibility.load( data, this );
 		}
 	}
 
@@ -453,10 +461,12 @@ public abstract class AbstractImmediateCollectionInitializer<Data extends Abstra
 		initializeSubInstancesFromParent( data );
 	}
 
-	protected abstract void readCollectionRow(
-			CollectionKey collectionKey,
-			List<Object> loadingState,
-			RowProcessingState rowProcessingState);
+	@Override
+	public void accept(Data data, List<Object> objects) {
+		readCollectionRow( data, objects );
+	}
+
+	protected abstract void readCollectionRow(Data data, List<Object> loadingState);
 
 	protected abstract void initializeSubInstancesFromParent(Data data);
 

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/ArrayInitializer.java

@@ -13,7 +13,6 @@ import java.util.function.BiConsumer;
 import org.hibernate.HibernateException;
 import org.hibernate.LockMode;
 import org.hibernate.collection.spi.PersistentArrayHolder;
-import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.internal.log.LoggingHelper;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.spi.NavigablePath;
@@ -86,10 +85,8 @@ public class ArrayInitializer extends AbstractImmediateCollectionInitializer<Abs
 	}
 
 	@Override
-	protected void readCollectionRow(
-			CollectionKey collectionKey,
-			List<Object> loadingState,
-			RowProcessingState rowProcessingState) {
+	protected void readCollectionRow(ImmediateCollectionInitializerData data, List<Object> loadingState) {
+		final RowProcessingState rowProcessingState = data.getRowProcessingState();
 		final Integer indexValue = listIndexAssembler.assemble( rowProcessingState );
 		if ( indexValue == null ) {
 			throw new HibernateException( "Illegal null value for array index encountered while reading: "

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/BagInitializer.java

@@ -13,7 +13,6 @@ import org.hibernate.LockMode;
 import org.hibernate.collection.spi.PersistentBag;
 import org.hibernate.collection.spi.PersistentCollection;
 import org.hibernate.collection.spi.PersistentIdentifierBag;
-import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.internal.log.LoggingHelper;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.spi.NavigablePath;
@@ -82,10 +81,8 @@ public class BagInitializer extends AbstractImmediateCollectionInitializer<Abstr
 	}
 
 	@Override
-	protected void readCollectionRow(
-			CollectionKey collectionKey,
-			List<Object> loadingState,
-			RowProcessingState rowProcessingState) {
+	protected void readCollectionRow(ImmediateCollectionInitializerData data, List<Object> loadingState) {
+		final RowProcessingState rowProcessingState = data.getRowProcessingState();
 		if ( collectionIdAssembler != null ) {
 			final Object collectionId = collectionIdAssembler.assemble( rowProcessingState );
 			if ( collectionId == null ) {

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/EagerCollectionFetch.java

@@ -209,6 +209,11 @@ public class EagerCollectionFetch extends CollectionFetch {
 		return true;
 	}
 
+	@Override
+	public int getCollectionFetchesCount() {
+		return 1 + super.getCollectionFetchesCount();
+	}
+
 	@Override
 	public JavaType<?> getResultJavaType() {
 		return getFetchedMapping().getJavaType();

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/ListInitializer.java

@@ -12,7 +12,6 @@ import java.util.function.BiConsumer;
 import org.hibernate.HibernateException;
 import org.hibernate.LockMode;
 import org.hibernate.collection.spi.PersistentList;
-import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.internal.log.LoggingHelper;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.spi.NavigablePath;
@@ -87,10 +86,8 @@ public class ListInitializer extends AbstractImmediateCollectionInitializer<Abst
 	}
 
 	@Override
-	protected void readCollectionRow(
-			CollectionKey collectionKey,
-			List<Object> loadingState,
-			RowProcessingState rowProcessingState) {
+	protected void readCollectionRow(ImmediateCollectionInitializerData data, List<Object> loadingState) {
+		final RowProcessingState rowProcessingState = data.getRowProcessingState();
 		final Integer indexValue = listIndexAssembler.assemble( rowProcessingState );
 		if ( indexValue == null ) {
 			throw new HibernateException( "Illegal null value for list index encountered while reading: "

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/MapInitializer.java

@@ -12,7 +12,6 @@ import java.util.function.BiConsumer;
 
 import org.hibernate.LockMode;
 import org.hibernate.collection.spi.PersistentMap;
-import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.internal.log.LoggingHelper;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.spi.NavigablePath;
@@ -90,10 +89,8 @@ public class MapInitializer extends AbstractImmediateCollectionInitializer<Abstr
 	}
 
 	@Override
-	protected void readCollectionRow(
-			CollectionKey collectionKey,
-			List<Object> loadingState,
-			RowProcessingState rowProcessingState) {
+	protected void readCollectionRow(ImmediateCollectionInitializerData data, List<Object> loadingState) {
+		final RowProcessingState rowProcessingState = data.getRowProcessingState();
 		final Object key = mapKeyAssembler.assemble( rowProcessingState );
 		if ( key == null ) {
 			// If element is null, then NotFoundAction must be IGNORE

hibernate-core/src/main/java/org/hibernate/sql/results/graph/collection/internal/SetInitializer.java

@@ -11,7 +11,6 @@ import java.util.function.BiConsumer;
 
 import org.hibernate.LockMode;
 import org.hibernate.collection.spi.PersistentSet;
-import org.hibernate.engine.spi.CollectionKey;
 import org.hibernate.internal.log.LoggingHelper;
 import org.hibernate.metamodel.mapping.PluralAttributeMapping;
 import org.hibernate.spi.NavigablePath;
@@ -77,10 +76,8 @@ public class SetInitializer extends AbstractImmediateCollectionInitializer<Abstr
 	}
 
 	@Override
-	protected void readCollectionRow(
-			CollectionKey collectionKey,
-			List<Object> loadingState,
-			RowProcessingState rowProcessingState) {
+	protected void readCollectionRow(ImmediateCollectionInitializerData data, List<Object> loadingState) {
+		final RowProcessingState rowProcessingState = data.getRowProcessingState();
 		final Object element = elementAssembler.assemble( rowProcessingState );
 		if ( element == null ) {
 			// If element is null, then NotFoundAction must be IGNORE

hibernate-core/src/main/java/org/hibernate/sql/results/graph/embeddable/internal/EmbeddableInitializerImpl.java

@@ -261,6 +261,22 @@ public class EmbeddableInitializerImpl extends AbstractInitializer<EmbeddableIni
 		}
 	}
 
+	@Override
+	public void resolveFromPreviousRow(EmbeddableInitializerData data) {
+		if ( data.getState() == State.UNINITIALIZED ) {
+			if ( data.getInstance() == null ) {
+				data.setState( State.MISSING );
+			}
+			else {
+				final RowProcessingState rowProcessingState = data.getRowProcessingState();
+				for ( Initializer<InitializerData> initializer : subInitializers[data.getSubclassId()] ) {
+					initializer.resolveFromPreviousRow( rowProcessingState );
+				}
+				data.setState( State.INITIALIZED );
+			}
+		}
+	}
+
 	@Override
 	public void resolveInstance(EmbeddableInitializerData data) {
 		if ( data.getState() != State.KEY_RESOLVED ) {

hibernate-core/src/main/java/org/hibernate/sql/results/graph/entity/internal/DiscriminatedEntityInitializer.java

@@ -126,6 +126,23 @@ public class DiscriminatedEntityInitializer
 		}
 	}
 
+	@Override
+	public void resolveFromPreviousRow(DiscriminatedEntityInitializerData data) {
+		if ( data.getState() == State.UNINITIALIZED ) {
+			if ( data.entityIdentifier == null ) {
+				data.setState( State.MISSING );
+				data.setInstance( null );
+			}
+			else {
+				final Initializer<?> initializer = keyValueAssembler.getInitializer();
+				if ( initializer != null ) {
+					initializer.resolveFromPreviousRow( data.getRowProcessingState() );
+				}
+				data.setState( State.INITIALIZED );
+			}
+		}
+	}
+
 	@Override
 	public void resolveInstance(DiscriminatedEntityInitializerData data) {
 		if ( data.getState() != State.KEY_RESOLVED ) {

hibernate-core/src/main/java/org/hibernate/sql/results/graph/entity/internal/EntityDelayedFetchInitializer.java

@@ -102,6 +102,23 @@ public class EntityDelayedFetchInitializer
 		return referencedModelPart;
 	}
 
+	@Override
+	public void resolveFromPreviousRow(EntityDelayedFetchInitializerData data) {
+		if ( data.getState() == State.UNINITIALIZED ) {
+			if ( data.entityIdentifier == null ) {
+				data.setState( State.MISSING );
+				data.setInstance( null );
+			}
+			else {
+				final Initializer<?> initializer = identifierAssembler.getInitializer();
+				if ( initializer != null ) {
+					initializer.resolveFromPreviousRow( data.getRowProcessingState() );
+				}
+				data.setState( State.RESOLVED );
+			}
+		}
+	}
+
 	@Override
 	public void resolveInstance(EntityDelayedFetchInitializerData data) {
 		if ( data.getState() != State.KEY_RESOLVED ) {

hibernate-core/src/main/java/org/hibernate/sql/results/graph/entity/internal/EntityInitializerImpl.java

@@ -63,6 +63,7 @@ import org.hibernate.sql.results.graph.Initializer;
 import org.hibernate.sql.results.graph.InitializerData;
 import org.hibernate.sql.results.graph.InitializerParent;
 import org.hibernate.sql.results.graph.basic.BasicResultAssembler;
+import org.hibernate.sql.results.graph.collection.internal.AbstractImmediateCollectionInitializer;
 import org.hibernate.sql.results.graph.entity.EntityInitializer;
 import org.hibernate.sql.results.graph.entity.EntityResultGraphNode;
 import org.hibernate.sql.results.graph.internal.AbstractInitializer;
@@ -106,6 +107,14 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 	private final boolean isPartOfKey;
 	private final boolean isResultInitializer;
 	private final boolean hasKeyManyToOne;
+	/**
+	 * Indicates whether there is a high chance of the previous row to have the same entity key as the current row
+	 * and hence enable a check in the {@link #resolveKey(RowProcessingState)} phase which compare the previously read
+	 * identifier with the current row identifier. If it matches, the state from the previous row processing can be reused.
+	 * In addition to that, all direct sub-initializers can be informed about the reuse by calling {@link Initializer#resolveFromPreviousRow(RowProcessingState)},
+	 * so that these initializers can avoid unnecessary processing as well.
+	 */
+	private final boolean previousRowReuse;
 
 	private final @Nullable DomainResultAssembler<?> keyAssembler;
 	private final @Nullable DomainResultAssembler<?> identifierAssembler;
@@ -163,6 +172,15 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 		this.parent = parent;
 		this.isResultInitializer = isResultInitializer;
 		this.isPartOfKey = Initializer.isPartOfKey( navigablePath, parent );
+		// If the parent already has previous row reuse enabled, we can skip that here
+		this.previousRowReuse = !isPreviousRowReuse( parent ) && (
+				// If this entity domain result contains a collection join fetch, this usually means that the entity data is
+				// duplicate in the result data for every collection element. Since collections usually have more than one element,
+				// optimizing the resolving of the entity data is very beneficial.
+				resultDescriptor.containsCollectionFetches()
+						// Result duplication generally also happens if more than one collection is join fetched,
+						|| creationState.containsMultipleCollectionFetches()
+		);
 
 		assert identifierFetch != null || isResultInitializer : "Identifier must be fetched, unless this is a result initializer";
 		if ( identifierFetch == null ) {
@@ -256,6 +274,21 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 		this.affectedByFilter = affectedByFilter;
 	}
 
+	private static boolean isPreviousRowReuse(@Nullable InitializerParent<?> parent) {
+		// Traverse up the parents to find out if one of our parents has row reuse enabled
+		while ( parent != null ) {
+			if ( parent instanceof EntityInitializerImpl ) {
+				return ( (EntityInitializerImpl) parent ).isPreviousRowReuse();
+			}
+			// Immediate collections don't reuse previous rows for elements, so we can safely assume false
+			if ( parent instanceof AbstractImmediateCollectionInitializer<?> ) {
+				return false;
+			}
+			parent = parent.getParent();
+		}
+		return false;
+	}
+
 	@Override
 	protected EntityInitializerData createInitializerData(RowProcessingState rowProcessingState) {
 		return new EntityInitializerData( rowProcessingState );
@@ -299,6 +332,10 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 		}
 		data.setState( State.KEY_RESOLVED );
 
+		final EntityKey oldEntityKey = data.entityKey;
+		final Object oldEntityInstance = data.getInstance();
+		final Object oldEntityInstanceForNotify = data.entityInstanceForNotify;
+		final EntityHolder oldEntityHolder = data.entityHolder;
 		// reset row state
 		data.concreteDescriptor = null;
 		data.entityKey = null;
@@ -344,6 +381,20 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 			}
 		}
 
+		if ( oldEntityKey != null && previousRowReuse && oldEntityInstance != null
+				&& entityDescriptor.getIdentifierType().isEqual( oldEntityKey.getIdentifier(), id ) ) {
+			// The row we read previously referred to this entity already, so we can safely assume it's initialized.
+			// Unfortunately we can't set the state to INITIALIZED though, as that has other implications,
+			// but RESOLVED is fine, since the EntityEntry is marked as initialized which skips instance initialization
+			data.setState( State.RESOLVED );
+			data.entityKey = oldEntityKey;
+			data.setInstance( oldEntityInstance );
+			data.entityInstanceForNotify = oldEntityInstanceForNotify;
+			data.concreteDescriptor = oldEntityKey.getPersister();
+			data.entityHolder = oldEntityHolder;
+			notifySubInitializersToReusePreviousRowInstance( data );
+			return;
+		}
 		resolveEntityKey( data, id );
 		if ( !entityKeyOnly ) {
 			// Resolve the entity instance early as we have no key many-to-one
@@ -413,6 +464,15 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 		}
 	}
 
+	private void notifySubInitializersToReusePreviousRowInstance(EntityInitializerData data) {
+		final RowProcessingState rowProcessingState = data.getRowProcessingState();
+		for ( Initializer<?> initializer : subInitializers[data.concreteDescriptor.getSubclassId()] ) {
+			if ( initializer != null ) {
+				initializer.resolveFromPreviousRow( rowProcessingState );
+			}
+		}
+	}
+
 	private void resolveKeySubInitializers(EntityInitializerData data) {
 		final RowProcessingState rowProcessingState = data.getRowProcessingState();
 		for ( Initializer<?> initializer : subInitializers[data.concreteDescriptor.getSubclassId()] ) {
@@ -467,6 +527,20 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 		}
 	}
 
+	@Override
+	public void resolveFromPreviousRow(EntityInitializerData data) {
+		if ( data.getState() == State.UNINITIALIZED ) {
+			final EntityKey entityKey = data.entityKey;
+			if ( entityKey == null ) {
+				setMissing( data );
+			}
+			else {
+				data.setState( State.RESOLVED );
+				notifySubInitializersToReusePreviousRowInstance( data );
+			}
+		}
+	}
+
 	@Override
 	public void initializeInstanceFromParent(Object parentInstance, EntityInitializerData data) {
 		final AttributeMapping attributeMapping = getInitializedPart().asAttributeMapping();
@@ -1384,6 +1458,10 @@ public class EntityInitializerImpl extends AbstractInitializer<EntityInitializer
 		return isPartOfKey;
 	}
 
+	public boolean isPreviousRowReuse() {
+		return previousRowReuse;
+	}
+
 	@Override
 	public EntityPersister getConcreteDescriptor(EntityInitializerData data) {
 		assert data.getState() != State.UNINITIALIZED;

hibernate-core/src/main/java/org/hibernate/sql/results/graph/entity/internal/EntitySelectFetchInitializer.java

@@ -104,6 +104,23 @@ public class EntitySelectFetchInitializer<Data extends EntitySelectFetchInitiali
 		return navigablePath;
 	}
 
+	@Override
+	public void resolveFromPreviousRow(Data data) {
+		if ( data.getState() == State.UNINITIALIZED ) {
+			if ( data.entityIdentifier == null ) {
+				data.setState( State.MISSING );
+				data.setInstance( null );
+			}
+			else {
+				final Initializer<?> initializer = keyAssembler.getInitializer();
+				if ( initializer != null ) {
+					initializer.resolveFromPreviousRow( data.getRowProcessingState() );
+				}
+				data.setState( State.INITIALIZED );
+			}
+		}
+	}
+
 	@Override
 	public void resolveInstance(Data data) {
 		if ( data.getState() != State.KEY_RESOLVED ) {

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

@@ -8,6 +8,7 @@ package org.hibernate.sql.results.internal;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
 import org.hibernate.collection.spi.PersistentCollection;
@@ -68,6 +69,11 @@ public class LoadingCollectionEntryImpl implements LoadingCollectionEntry {
 		loadingEntryConsumer.accept( loadingState );
 	}
 
+	@Override
+	public <T> void load(T arg1, BiConsumer<T, List<Object>> loadingEntryConsumer) {
+		loadingEntryConsumer.accept( arg1, loadingState );
+	}
+
 	@Override public void finishLoading(ExecutionContext executionContext) {
 		collectionInstance.injectLoadedState(
 				getCollectionDescriptor().getAttributeMapping(),

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

@@ -109,6 +109,7 @@ public class StandardJdbcValuesMapping implements JdbcValuesMapping {
 		private int initializerId;
 		boolean hasCollectionInitializers;
 		Boolean dynamicInstantiation;
+		Boolean containsMultipleCollectionFetches;
 
 		public AssemblerCreationStateImpl(
 				JdbcValuesMapping jdbcValuesMapping,
@@ -127,6 +128,20 @@ public class StandardJdbcValuesMapping implements JdbcValuesMapping {
 			return dynamicInstantiation;
 		}
 
+		@Override
+		public boolean containsMultipleCollectionFetches() {
+			if ( containsMultipleCollectionFetches == null ) {
+				int collectionFetchesCount = 0;
+				for ( DomainResult<?> domainResult : jdbcValuesMapping.getDomainResults() ) {
+					if ( domainResult instanceof FetchParent ) {
+						collectionFetchesCount += ( (FetchParent) domainResult ).getCollectionFetchesCount();
+					}
+				}
+				containsMultipleCollectionFetches = collectionFetchesCount > 1;
+			}
+			return containsMultipleCollectionFetches;
+		}
+
 		@Override
 		public int acquireInitializerId() {
 			return initializerId++;

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/collections/ElementCollectionCachePerfTest.java

@@ -0,0 +1,328 @@
+/*
+ * 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.mapping.collections;
+
+import java.util.AbstractMap;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.jpa.AvailableHints;
+
+import org.hibernate.testing.orm.junit.EntityManagerFactoryScope;
+import org.hibernate.testing.orm.junit.Jira;
+import org.hibernate.testing.orm.junit.Jpa;
+import org.hibernate.testing.orm.junit.Setting;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.ElementCollection;
+import jakarta.persistence.Embeddable;
+import jakarta.persistence.Embedded;
+import jakarta.persistence.Entity;
+import jakarta.persistence.EntityManager;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.Id;
+import jakarta.persistence.ManyToOne;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@Jpa(
+		annotatedClasses = {
+				ElementCollectionCachePerfTest.Element.class,
+				ElementCollectionCachePerfTest.KeyValue.class,
+				ElementCollectionCachePerfTest.Association.class,
+		},
+		properties = {
+				@Setting(name = AvailableSettings.USE_QUERY_CACHE, value = "true"),
+				@Setting(name = AvailableSettings.USE_SECOND_LEVEL_CACHE, value = "true"),
+				@Setting(name = AvailableSettings.QUERY_CACHE_LAYOUT, value = "auto")
+		}
+)
+@Jira("https://hibernate.atlassian.net/browse/HHH-18375")
+public class ElementCollectionCachePerfTest {
+	@BeforeAll
+	public void setUp(EntityManagerFactoryScope scope) {
+		scope.inTransaction( entityManager -> {
+			for ( int i = 0; i < 100; i++ ) {
+				final String id = UUID.randomUUID().toString();
+				final Element element = new Element( id );
+				element.setKeyValueEmbeddable( new KeyValue( "embeddable", "_" + id ) );
+				element.setAssociation1( new Association( (long) i, "assoc_" + id ) );
+
+				final Set<KeyValue> key1Values = new HashSet<>();
+				key1Values.add( new KeyValue( "key1_1", "_" + id ) );
+				key1Values.add( new KeyValue( "key1_2", "_" + id ) );
+				key1Values.add( new KeyValue( "key1_3", "_" + id ) );
+				element.setKeyValues1( key1Values );
+
+				final Set<KeyValue> key2Values = new HashSet<>();
+				key2Values.add( new KeyValue( "key2_1", "_" + id ) );
+				key2Values.add( new KeyValue( "key2_2", "_" + id ) );
+				element.setKeyValues2( key2Values );
+
+				final Map<String, KeyValue> map = new HashMap<>();
+				map.put( "k1", new KeyValue( "k1", "_" + id ) );
+				map.put( "k2", new KeyValue( "k2", "_" + id ) );
+				element.setMap( map );
+
+				entityManager.persist( element );
+			}
+		} );
+	}
+
+	@Test
+	public void testSelect1(EntityManagerFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					assertQuery(
+							entityManager,
+							"select e from Element e join fetch e.association1 join fetch e.keyValues1 join fetch e.keyValues2 join fetch e.map"
+					);
+				} );
+	}
+
+	@Test
+	public void testSelect2(EntityManagerFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					assertQuery(
+							entityManager,
+							"select e from Element e join fetch e.association1 join fetch e.map join fetch e.keyValues1 join fetch e.keyValues2"
+					);
+				} );
+	}
+
+	private static void assertQuery(EntityManager entityManager, String query) {
+		final List<Element> firstResult = entityManager.createQuery( query, Element.class )
+				.setHint( AvailableHints.HINT_CACHEABLE, true )
+				.getResultList();
+		assertResults( firstResult );
+		final List<Element> secondResult = entityManager.createQuery( query, Element.class )
+				.setHint( AvailableHints.HINT_CACHEABLE, true )
+				.getResultList();
+		assertResults( secondResult );
+	}
+
+	private static void assertResults(List<Element> result) {
+		for ( Element element : result ) {
+			final String id = element.getId();
+			assertThat( element.getAssociation1().getName() ).isEqualTo( "assoc_" + id );
+			assertThat( element.getKeyValueEmbeddable().getK() ).isEqualTo( "embeddable" );
+			assertThat( element.getKeyValueEmbeddable().getV() ).isEqualTo( "_" + id );
+			assertThat( element.getKeyValues1().size() ).isEqualTo( 3 );
+			assertThat( element.getKeyValues2().size() ).isEqualTo( 2 );
+			assertThat( element.getMap().size() ).isEqualTo( 2 );
+			assertThat( element.getKeyValues1() ).containsExactlyInAnyOrder(
+					new KeyValue( "key1_1", "_" + id ),
+					new KeyValue( "key1_2", "_" + id ),
+					new KeyValue( "key1_3", "_" + id )
+			);
+			assertThat( element.getKeyValues2() ).containsExactlyInAnyOrder(
+					new KeyValue( "key2_1", "_" + id ),
+					new KeyValue( "key2_2", "_" + id )
+			);
+			assertThat( element.getMap() ).containsExactly(
+					new AbstractMap.SimpleEntry<>( "k1", new KeyValue( "k1", "_" + id ) ),
+					new AbstractMap.SimpleEntry<>( "k2", new KeyValue( "k2", "_" + id ) )
+			);
+		}
+	}
+
+	@Entity(name = "Element")
+	public static class Element {
+		@Id
+		private String id;
+
+		@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
+		private Association association1;
+
+		@Embedded
+		KeyValue keyValueEmbeddable;
+
+		@ElementCollection
+		private Set<KeyValue> keyValues1;
+
+		@ElementCollection
+		private Set<KeyValue> keyValues2;
+
+		@ElementCollection
+		private Map<String, KeyValue> map;
+
+		protected Element() {
+		}
+
+		public Element(String id) {
+			this.id = id;
+		}
+
+		public String getId() {
+			return id;
+		}
+
+		public void setId(String id) {
+			this.id = id;
+		}
+
+		public Association getAssociation1() {
+			return association1;
+		}
+
+		public void setAssociation1(Association association1) {
+			this.association1 = association1;
+		}
+
+		public KeyValue getKeyValueEmbeddable() {
+			return keyValueEmbeddable;
+		}
+
+		public void setKeyValueEmbeddable(KeyValue keyValueEmbeddable) {
+			this.keyValueEmbeddable = keyValueEmbeddable;
+		}
+
+		public Set<KeyValue> getKeyValues1() {
+			return keyValues1;
+		}
+
+		public void setKeyValues1(Set<KeyValue> keyValues) {
+			this.keyValues1 = keyValues;
+		}
+
+		public Set<KeyValue> getKeyValues2() {
+			return keyValues2;
+		}
+
+		public void setKeyValues2(Set<KeyValue> keyValues2) {
+			this.keyValues2 = keyValues2;
+		}
+
+		public Map<String, KeyValue> getMap() {
+			return map;
+		}
+
+		public void setMap(Map<String, KeyValue> map) {
+			this.map = map;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if ( this == o ) {
+				return true;
+			}
+			if ( o == null || getClass() != o.getClass() ) {
+				return false;
+			}
+			Element element = (Element) o;
+			return Objects.equals( id, element.id );
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hash( id );
+		}
+
+		@Override
+		public String toString() {
+			return "Element{" +
+					"id=" + id +
+					", keyValues=" + keyValues1 +
+					'}';
+		}
+	}
+
+	@Embeddable
+	public static class KeyValue {
+		private String k;
+		private String v;
+
+		public KeyValue() {
+		}
+
+		public KeyValue(String k, String v) {
+			this.k = k;
+			this.v = v;
+		}
+
+		public String getK() {
+			return k;
+		}
+
+		public void setK(String key) {
+			this.k = key;
+		}
+
+		public String getV() {
+			return v;
+		}
+
+		public void setV(String value) {
+			this.v = value;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if ( this == o ) {
+				return true;
+			}
+			if ( o == null || getClass() != o.getClass() ) {
+				return false;
+			}
+			KeyValue keyValue = (KeyValue) o;
+			return Objects.equals( k, keyValue.k ) && Objects.equals( v, keyValue.v );
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hash( k, v );
+		}
+
+		@Override
+		public String toString() {
+			return "KeyValue{" +
+					"key='" + k + '\'' +
+					", value='" + v + '\'' +
+					'}';
+		}
+	}
+
+	@Entity(name = "Association")
+	public static class Association {
+		@Id
+		private Long id;
+		private String name;
+
+		public Association() {
+		}
+
+		public Association(Long id, String name) {
+			this.id = id;
+			this.name = name;
+		}
+
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+}

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/collections/ElementCollectionPerfTest.java

@@ -0,0 +1,341 @@
+/*
+ * 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.mapping.collections;
+
+import java.util.AbstractMap;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+import org.hibernate.testing.orm.junit.Jira;
+import org.hibernate.testing.orm.junit.Jpa;
+import org.hibernate.testing.orm.junit.EntityManagerFactoryScope;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.ElementCollection;
+import jakarta.persistence.Embeddable;
+import jakarta.persistence.Embedded;
+import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.Id;
+import jakarta.persistence.ManyToOne;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@Jpa(annotatedClasses = {
+		ElementCollectionPerfTest.Element.class,
+		ElementCollectionPerfTest.KeyValue.class,
+		ElementCollectionPerfTest.Association.class,
+})
+@Jira("https://hibernate.atlassian.net/browse/HHH-18375")
+public class ElementCollectionPerfTest {
+	@BeforeAll
+	public void setUp(EntityManagerFactoryScope scope) {
+		scope.inTransaction( entityManager -> {
+			for ( int i = 0; i < 100; i++ ) {
+				final String id = UUID.randomUUID().toString();
+				final Element element = new Element( id );
+				element.setKeyValueEmbeddable( new KeyValue( "embeddable", "_" + id ) );
+				element.setAssociation1( new Association( (long) i, "assoc_" + id ) );
+
+				final Set<KeyValue> key1Values = new HashSet<>();
+				key1Values.add( new KeyValue( "key1_1", "_" + id ) );
+				key1Values.add( new KeyValue( "key1_2", "_" + id ) );
+				key1Values.add( new KeyValue( "key1_3", "_" + id ) );
+				element.setKeyValues1( key1Values );
+
+				element.association1.keyValues1 = new HashSet<>( key1Values);
+
+				final Set<KeyValue> key2Values = new HashSet<>();
+				key2Values.add( new KeyValue( "key2_1", "_" + id ) );
+				key2Values.add( new KeyValue( "key2_2", "_" + id ) );
+				element.setKeyValues2( key2Values );
+
+				final Map<String, KeyValue> map = new HashMap<>();
+				map.put( "k1", new KeyValue( "k1", "_" + id ) );
+				map.put( "k2", new KeyValue( "k2", "_" + id ) );
+				element.setMap( map );
+
+				entityManager.persist( element );
+			}
+		} );
+	}
+
+	@Test
+	public void testSelect0(EntityManagerFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					List<Element> result = entityManager.createQuery(
+							"select e from Element e join fetch e.association1 a join fetch a.keyValues1 join fetch e.keyValues1 join fetch e.keyValues2 join fetch e.map",
+							Element.class
+					).getResultList();
+
+					assertResults( result );
+				} );
+	}
+
+	@Test
+	public void testSelect1(EntityManagerFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					List<Element> result = entityManager.createQuery(
+							"select e from Element e join fetch e.association1 join fetch e.keyValues1 join fetch e.keyValues2 join fetch e.map",
+							Element.class
+					).getResultList();
+
+					assertResults( result );
+				} );
+	}
+
+	@Test
+	public void testSelect2(EntityManagerFactoryScope scope) {
+		scope.inTransaction(
+				entityManager -> {
+					List<Element> result = entityManager.createQuery(
+							"select e from Element e join fetch e.association1 join fetch e.map join fetch e.keyValues1 join fetch e.keyValues2",
+							Element.class
+					).getResultList();
+
+					assertResults( result );
+				} );
+	}
+
+	private static void assertResults(List<Element> result) {
+		for ( Element element : result ) {
+			final String id = element.getId();
+			assertThat( element.getAssociation1().getName() ).isEqualTo( "assoc_" + id );
+			assertThat( element.getAssociation1().getKeyValues1().size() ).isEqualTo( 3 );
+			assertThat( element.getKeyValueEmbeddable().getK() ).isEqualTo( "embeddable" );
+			assertThat( element.getKeyValueEmbeddable().getV() ).isEqualTo( "_" + id );
+			assertThat( element.getKeyValues1().size() ).isEqualTo( 3 );
+			assertThat( element.getKeyValues2().size() ).isEqualTo( 2 );
+			assertThat( element.getMap().size() ).isEqualTo( 2 );
+			assertThat( element.getAssociation1().getKeyValues1() ).containsExactlyInAnyOrder(
+					new KeyValue( "key1_1", "_" + id ),
+					new KeyValue( "key1_2", "_" + id ),
+					new KeyValue( "key1_3", "_" + id )
+			);
+			assertThat( element.getKeyValues1() ).containsExactlyInAnyOrder(
+					new KeyValue( "key1_1", "_" + id ),
+					new KeyValue( "key1_2", "_" + id ),
+					new KeyValue( "key1_3", "_" + id )
+			);
+			assertThat( element.getKeyValues2() ).containsExactlyInAnyOrder(
+					new KeyValue( "key2_1", "_" + id ),
+					new KeyValue( "key2_2", "_" + id )
+			);
+			assertThat( element.getMap() ).containsExactly(
+					new AbstractMap.SimpleEntry<>( "k1", new KeyValue( "k1", "_" + id ) ),
+					new AbstractMap.SimpleEntry<>( "k2", new KeyValue( "k2", "_" + id ) )
+			);
+		}
+	}
+
+	@Entity(name = "Element")
+	public static class Element {
+		@Id
+		private String id;
+
+		@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
+		private Association association1;
+
+		@Embedded
+		KeyValue keyValueEmbeddable;
+
+		@ElementCollection
+		private Set<KeyValue> keyValues1;
+
+		@ElementCollection
+		private Set<KeyValue> keyValues2;
+
+		@ElementCollection
+		private Map<String, KeyValue> map;
+
+		protected Element() {
+		}
+
+		public Element(String id) {
+			this.id = id;
+		}
+
+		public String getId() {
+			return id;
+		}
+
+		public void setId(String id) {
+			this.id = id;
+		}
+
+		public Association getAssociation1() {
+			return association1;
+		}
+
+		public void setAssociation1(Association association1) {
+			this.association1 = association1;
+		}
+
+		public KeyValue getKeyValueEmbeddable() {
+			return keyValueEmbeddable;
+		}
+
+		public void setKeyValueEmbeddable(KeyValue keyValueEmbeddable) {
+			this.keyValueEmbeddable = keyValueEmbeddable;
+		}
+
+		public Set<KeyValue> getKeyValues1() {
+			return keyValues1;
+		}
+
+		public void setKeyValues1(Set<KeyValue> keyValues) {
+			this.keyValues1 = keyValues;
+		}
+
+		public Set<KeyValue> getKeyValues2() {
+			return keyValues2;
+		}
+
+		public void setKeyValues2(Set<KeyValue> keyValues2) {
+			this.keyValues2 = keyValues2;
+		}
+
+		public Map<String, KeyValue> getMap() {
+			return map;
+		}
+
+		public void setMap(Map<String, KeyValue> map) {
+			this.map = map;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if ( this == o ) {
+				return true;
+			}
+			if ( o == null || getClass() != o.getClass() ) {
+				return false;
+			}
+			Element element = (Element) o;
+			return Objects.equals( id, element.id );
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hash( id );
+		}
+
+		@Override
+		public String toString() {
+			return "Element{" +
+					"id=" + id +
+					", keyValues=" + keyValues1 +
+					'}';
+		}
+	}
+
+	@Embeddable
+	public static class KeyValue {
+		private String k;
+		private String v;
+
+		public KeyValue() {
+		}
+
+		public KeyValue(String k, String v) {
+			this.k = k;
+			this.v = v;
+		}
+
+		public String getK() {
+			return k;
+		}
+
+		public void setK(String key) {
+			this.k = key;
+		}
+
+		public String getV() {
+			return v;
+		}
+
+		public void setV(String value) {
+			this.v = value;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if ( this == o ) {
+				return true;
+			}
+			if ( o == null || getClass() != o.getClass() ) {
+				return false;
+			}
+			KeyValue keyValue = (KeyValue) o;
+			return Objects.equals( k, keyValue.k ) && Objects.equals( v, keyValue.v );
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hash( k, v );
+		}
+
+		@Override
+		public String toString() {
+			return "KeyValue{" +
+					"key='" + k + '\'' +
+					", value='" + v + '\'' +
+					'}';
+		}
+	}
+
+	@Entity(name = "Association")
+	public static class Association {
+		@Id
+		private Long id;
+		private String name;
+
+		@ElementCollection
+		private Set<KeyValue> keyValues1;
+
+		public Association() {
+		}
+
+		public Association(Long id, String name) {
+			this.id = id;
+			this.name = name;
+		}
+
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public Set<KeyValue> getKeyValues1() {
+			return keyValues1;
+		}
+
+		public void setKeyValues1(Set<KeyValue> keyValues1) {
+			this.keyValues1 = keyValues1;
+		}
+	}
+}