HHH-12558 - Lazy load EntityLoaders to improve memory usage

hibernate-core/src/main/java/org/hibernate/boot/SessionFactoryBuilder.java

@@ -6,6 +6,9 @@
  */
 package org.hibernate.boot;
 
+import java.util.Map;
+import java.util.function.Supplier;
+
 import org.hibernate.ConnectionReleaseMode;
 import org.hibernate.CustomEntityDirtinessStrategy;
 import org.hibernate.EntityMode;
@@ -27,9 +30,6 @@
 import org.hibernate.tuple.entity.EntityTuplizer;
 import org.hibernate.tuple.entity.EntityTuplizerFactory;
 
-import java.util.Map;
-import java.util.function.Supplier;
-
 /**
  * The contract for building a {@link org.hibernate.SessionFactory} given a number of options.
  *
@@ -303,6 +303,14 @@ SessionFactoryBuilder applyEntityTuplizer(
 	 */
 	SessionFactoryBuilder applyBatchFetchStyle(BatchFetchStyle style);
 
+	/**
+	 * Should entity Loaders be generated immediately?  Or should the creation
+	 * be delayed until first need?
+	 *
+	 * @see org.hibernate.cfg.AvailableSettings#DELAY_ENTITY_LOADER_CREATIONS
+	 */
+	SessionFactoryBuilder applyDelayedEntityLoaderCreations(boolean delay);
+
 	/**
 	 * Allows specifying a default batch-fetch size for all entities and collections
 	 * which do not otherwise specify a batch-fetch size.

hibernate-core/src/main/java/org/hibernate/boot/internal/SessionFactoryBuilderImpl.java

@@ -219,6 +219,12 @@ public SessionFactoryBuilder applyBatchFetchStyle(BatchFetchStyle style) {
 		return this;
 	}
 
+	@Override
+	public SessionFactoryBuilder applyDelayedEntityLoaderCreations(boolean delay) {
+		this.optionsBuilder.applyDelayedEntityLoaderCreations( delay );
+		return this;
+	}
+
 	@Override
 	public SessionFactoryBuilder applyDefaultBatchFetchSize(int size) {
 		this.optionsBuilder.applyDefaultBatchFetchSize( size );

hibernate-core/src/main/java/org/hibernate/boot/internal/SessionFactoryOptionsBuilder.java

@@ -82,6 +82,7 @@
 import static org.hibernate.cfg.AvailableSettings.CUSTOM_ENTITY_DIRTINESS_STRATEGY;
 import static org.hibernate.cfg.AvailableSettings.DEFAULT_BATCH_FETCH_SIZE;
 import static org.hibernate.cfg.AvailableSettings.DEFAULT_ENTITY_MODE;
+import static org.hibernate.cfg.AvailableSettings.DELAY_ENTITY_LOADER_CREATIONS;
 import static org.hibernate.cfg.AvailableSettings.ENABLE_LAZY_LOAD_NO_TRANS;
 import static org.hibernate.cfg.AvailableSettings.FAIL_ON_PAGINATION_OVER_COLLECTION_FETCH;
 import static org.hibernate.cfg.AvailableSettings.FLUSH_BEFORE_COMPLETION;
@@ -183,6 +184,7 @@ public class SessionFactoryOptionsBuilder implements SessionFactoryOptions {
 	private MultiTableBulkIdStrategy multiTableBulkIdStrategy;
 	private TempTableDdlTransactionHandling tempTableDdlTransactionHandling;
 	private BatchFetchStyle batchFetchStyle;
+	private boolean delayBatchFetchLoaderCreations;
 	private int defaultBatchFetchSize;
 	private Integer maximumFetchDepth;
 	private NullPrecedence defaultNullPrecedence;
@@ -324,6 +326,7 @@ public SessionFactoryOptionsBuilder(StandardServiceRegistry serviceRegistry, Boo
 		);
 
 		this.batchFetchStyle = BatchFetchStyle.interpret( configurationSettings.get( BATCH_FETCH_STYLE ) );
+		this.delayBatchFetchLoaderCreations = cfgService.getSetting( DELAY_ENTITY_LOADER_CREATIONS, BOOLEAN, true );
 		this.defaultBatchFetchSize = ConfigurationHelper.getInt( DEFAULT_BATCH_FETCH_SIZE, configurationSettings, -1 );
 		this.maximumFetchDepth = ConfigurationHelper.getInteger( MAX_FETCH_DEPTH, configurationSettings );
 		final String defaultNullPrecedence = ConfigurationHelper.getString(
@@ -773,6 +776,11 @@ public BatchFetchStyle getBatchFetchStyle() {
 		return batchFetchStyle;
 	}
 
+	@Override
+	public boolean isDelayBatchFetchLoaderCreationsEnabled() {
+		return delayBatchFetchLoaderCreations;
+	}
+
 	@Override
 	public int getDefaultBatchFetchSize() {
 		return defaultBatchFetchSize;
@@ -1110,6 +1118,10 @@ public void applyBatchFetchStyle(BatchFetchStyle style) {
 		this.batchFetchStyle = style;
 	}
 
+	public void applyDelayedEntityLoaderCreations(boolean delay) {
+		this.delayBatchFetchLoaderCreations = delay;
+	}
+
 	public void applyDefaultBatchFetchSize(int size) {
 		this.defaultBatchFetchSize = size;
 	}
@@ -1300,5 +1312,4 @@ public SessionFactoryOptions buildOptions() {
 
 		return this;
 	}
-
 }

hibernate-core/src/main/java/org/hibernate/boot/spi/AbstractDelegatingSessionFactoryBuilder.java

@@ -6,6 +6,9 @@
  */
 package org.hibernate.boot.spi;
 
+import java.util.Map;
+import java.util.function.Supplier;
+
 import org.hibernate.ConnectionReleaseMode;
 import org.hibernate.CustomEntityDirtinessStrategy;
 import org.hibernate.EntityMode;
@@ -28,9 +31,6 @@
 import org.hibernate.tuple.entity.EntityTuplizer;
 import org.hibernate.tuple.entity.EntityTuplizerFactory;
 
-import java.util.Map;
-import java.util.function.Supplier;
-
 /**
  * Convenience base class for custom implementors of SessionFactoryBuilder, using delegation
  *
@@ -193,6 +193,12 @@ public T applyBatchFetchStyle(BatchFetchStyle style) {
 		return getThis();
 	}
 
+	@Override
+	public SessionFactoryBuilder applyDelayedEntityLoaderCreations(boolean delay) {
+		delegate.applyDelayedEntityLoaderCreations( delay );
+		return getThis();
+	}
+
 	@Override
 	public T applyDefaultBatchFetchSize(int size) {
 		delegate.applyDefaultBatchFetchSize( size );

hibernate-core/src/main/java/org/hibernate/boot/spi/AbstractDelegatingSessionFactoryOptions.java

@@ -6,6 +6,10 @@
  */
 package org.hibernate.boot.spi;
 
+import java.util.Map;
+import java.util.TimeZone;
+import java.util.function.Supplier;
+
 import org.hibernate.ConnectionReleaseMode;
 import org.hibernate.CustomEntityDirtinessStrategy;
 import org.hibernate.EntityMode;
@@ -31,10 +35,6 @@
 import org.hibernate.resource.jdbc.spi.StatementInspector;
 import org.hibernate.tuple.entity.EntityTuplizerFactory;
 
-import java.util.Map;
-import java.util.TimeZone;
-import java.util.function.Supplier;
-
 /**
  * Convenience base class for custom implementors of SessionFactoryOptions, using delegation
  *
@@ -172,6 +172,11 @@ public BatchFetchStyle getBatchFetchStyle() {
 		return delegate.getBatchFetchStyle();
 	}
 
+	@Override
+	public boolean isDelayBatchFetchLoaderCreationsEnabled() {
+		return delegate.isDelayBatchFetchLoaderCreationsEnabled();
+	}
+
 	@Override
 	public int getDefaultBatchFetchSize() {
 		return delegate.getDefaultBatchFetchSize();

hibernate-core/src/main/java/org/hibernate/boot/spi/SessionFactoryOptions.java

@@ -161,6 +161,8 @@ default Supplier<? extends Interceptor> getStatelessInterceptorImplementorSuppli
 
 	BatchFetchStyle getBatchFetchStyle();
 
+	boolean isDelayBatchFetchLoaderCreationsEnabled();
+
 	int getDefaultBatchFetchSize();
 
 	Integer getMaximumFetchDepth();

hibernate-core/src/main/java/org/hibernate/cfg/AvailableSettings.java

@@ -7,7 +7,6 @@
 package org.hibernate.cfg;
 
 import java.util.function.Supplier;
-
 import javax.persistence.GeneratedValue;
 
 import org.hibernate.HibernateException;
@@ -1560,6 +1559,20 @@ public interface AvailableSettings extends org.hibernate.jpa.AvailableSettings {
 	 */
 	String BATCH_FETCH_STYLE = "hibernate.batch_fetch_style";
 
+	/**
+	 * Controls how the individual Loaders for an entity are created.
+	 *
+	 * When `true` (the default), only the minimal set of Loaders are
+	 * created.  These include the handling for {@link org.hibernate.LockMode#READ}
+	 * and {@link org.hibernate.LockMode#NONE} as well as specialized Loaders for
+	 * merge and refresh handling.
+	 *
+	 * `false` indicates that all loaders should be created up front
+	 *
+	 * @since 5.3
+	 */
+	String DELAY_ENTITY_LOADER_CREATIONS = "hibernate.loader.delay_entity_loader_creations";
+
 	/**
 	 * A transaction can be rolled back by another thread ("tracking by thread")
 	 * -- not the original application. Examples of this include a JTA
@@ -1922,4 +1935,5 @@ public interface AvailableSettings extends org.hibernate.jpa.AvailableSettings {
 	 * @since 5.2.17
 	 */
 	String IN_CLAUSE_PARAMETER_PADDING = "hibernate.query.in_clause_parameter_padding";
+
 }

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

@@ -14,11 +14,13 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Comparator;
+import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -4113,7 +4115,12 @@ public final void postInstantiate() throws MappingException {
 	protected void doPostInstantiate() {
 	}
 
-	//needed by subclasses to override the createLoader strategy
+	/**
+	 * "Needed" by subclasses to override the createLoader strategy
+	 *
+	 * @deprecated Because there are better patterns for this
+	 */
+	@Deprecated
 	protected Map getLoaders() {
 		return loaders;
 	}
@@ -4125,9 +4132,17 @@ protected void createLoaders() {
 		noneLockLoader = createEntityLoader( LockMode.NONE );
 		readLockLoader = createEntityLoader( LockMode.READ );
 
-		final Map loaders = getLoaders();
 
-		// The loaders for the other lock modes are lazily loaded and will later be stored in this map.
+		// The loaders for the other lock modes are lazily loaded and will later be stored in this map,
+		//		unless this setting is disabled
+		if ( ! factory.getSessionFactoryOptions().isDelayBatchFetchLoaderCreationsEnabled() ) {
+			for ( LockMode lockMode : EnumSet.complementOf( EnumSet.of( LockMode.NONE, LockMode.READ ) ) ) {
+				loaders.put( lockMode, createEntityLoader( lockMode ) );
+			}
+		}
+
+
+		// And finally, create the internal merge and refresh load plans
 
 		loaders.put(
 				"merge",
@@ -4147,10 +4162,10 @@ else if ( LockMode.READ == lockMode ) {
 			return readLockLoader;
 		}
 
-		return loaders.computeIfAbsent( lockMode, this::createLazyLoadedEntityLoader );
+		return loaders.computeIfAbsent( lockMode, this::generateDelayedEntityLoader );
 	}
 
-	private UniqueEntityLoader createLazyLoadedEntityLoader(Object lockModeObject) {
+	private UniqueEntityLoader generateDelayedEntityLoader(Object lockModeObject) {
 		// Unfortunately, the loaders map mixes LockModes and Strings as keys so we need to accept an Object.
 		// The cast is safe as we will always call this method with a LockMode.
 		LockMode lockMode = (LockMode) lockModeObject;
@@ -4159,23 +4174,26 @@ private UniqueEntityLoader createLazyLoadedEntityLoader(Object lockModeObject) {
 			case NONE:
 			case READ:
 			case OPTIMISTIC:
-			case OPTIMISTIC_FORCE_INCREMENT:
+			case OPTIMISTIC_FORCE_INCREMENT: {
 				return createEntityLoader( lockMode );
+			}
 			case UPGRADE:
 			case UPGRADE_NOWAIT:
 			case UPGRADE_SKIPLOCKED:
 			case FORCE:
 			case PESSIMISTIC_READ:
 			case PESSIMISTIC_WRITE:
-			case PESSIMISTIC_FORCE_INCREMENT:
+			case PESSIMISTIC_FORCE_INCREMENT: {
 				//TODO: inexact, what we really need to know is: are any outer joins used?
-				boolean disableForUpdate = getSubclassTableSpan() > 1 &&
+				boolean disableForUpdate = getSubclassTableSpan() > 1
-						hasSubclasses() &&
+						&& hasSubclasses()
-						!getFactory().getDialect().supportsOuterJoinForUpdate();
+						&& !getFactory().getDialect().supportsOuterJoinForUpdate();
 
 				return disableForUpdate ? readLockLoader : createEntityLoader( lockMode );
-			default:
+			}
-				throw new IllegalStateException( String.format( "Lock mode %1$s not supported by entity loaders.", lockMode ) );
+			default: {
+				throw new IllegalStateException( String.format( Locale.ROOT, "Lock mode %1$s not supported by entity loaders.", lockMode ) );
+			}
 		}
 	}
 
@@ -4258,7 +4276,7 @@ else if ( session.getLoadQueryInfluencers().getInternalFetchProfile() != null &&
 			// Next, we consider whether an 'internal' fetch profile has been set.
 			// This indicates a special fetch profile Hibernate needs applied
 			// (for its merge loading process e.g.).
-			return (UniqueEntityLoader) getLoaders().get( session.getLoadQueryInfluencers().getInternalFetchProfile() );
+			return loaders.get( session.getLoadQueryInfluencers().getInternalFetchProfile() );
 		}
 		else if ( isAffectedByEnabledFetchProfiles( session ) ) {
 			// If the session has associated influencers we need to adjust the
@@ -4272,7 +4290,7 @@ else if ( lockOptions.getTimeOut() != LockOptions.WAIT_FOREVER ) {
 			return createEntityLoader( lockOptions, session.getLoadQueryInfluencers() );
 		}
 		else {
-			return (UniqueEntityLoader) getLoaderByLockMode( lockOptions.getLockMode() );
+			return getLoaderByLockMode( lockOptions.getLockMode() );
 		}
 	}