HHH-19668 Reduce size of collections held in ParameterInterpretationImpl before storing them in the cache

Instances of ParameterInterpretationImpl are being held in the interpretation cache for native queries. We had reports of these elements having a substantial impact on memory consumption.

A simple improvement is to ensure the collections being held on by the container object are minimized; some more substantial improvements could also be investigated but I’ll leave those for another time.

Author: Sanne

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

@@ -343,6 +343,9 @@ public static <T> Set<T> toSmallSet(Set<T> set) {
 	 * The goal is to save memory.
 	 */
 	public static <K, V> Map<K, V> toSmallMap(final Map<K, V> map) {
+		if ( map == null ) {
+			return emptyMap();
+		}
 		return switch ( map.size() ) {
 			case 0 -> emptyMap();
 			case 1 -> {
@@ -363,6 +366,9 @@ public static <K, V> Map<K, V> toSmallMap(final Map<K, V> map) {
 	 * The goal is to save memory.
 	 */
 	public static <V> List<V> toSmallList(ArrayList<V> arrayList) {
+		if ( arrayList == null ) {
+			return emptyList();
+		}
 		return switch ( arrayList.size() ) {
 			case 0 -> emptyList();
 			case 1 -> singletonList( arrayList.get( 0 ) );

hibernate-core/src/main/java/org/hibernate/query/sql/internal/NativeQueryImpl.java

@@ -128,6 +128,8 @@
 import static org.hibernate.internal.util.collections.CollectionHelper.isEmpty;
 import static org.hibernate.internal.util.collections.CollectionHelper.isNotEmpty;
 import static org.hibernate.internal.util.collections.CollectionHelper.makeCopy;
+import static org.hibernate.internal.util.collections.CollectionHelper.toSmallList;
+import static org.hibernate.internal.util.collections.CollectionHelper.toSmallMap;
 import static org.hibernate.internal.util.type.PrimitiveWrapperHelper.getDescriptorByPrimitiveType;
 import static org.hibernate.jpa.HibernateHints.HINT_NATIVE_LOCK_MODE;
 import static org.hibernate.query.results.internal.Builders.resultClassBuilder;
@@ -1742,9 +1744,9 @@ private static class ParameterInterpretationImpl implements ParameterInterpretat
 
 		public ParameterInterpretationImpl(ParameterRecognizerImpl parameterRecognizer) {
 			this.sqlString = parameterRecognizer.getAdjustedSqlString();
-			this.parameterList = parameterRecognizer.getParameterList();
-			this.positionalParameters = parameterRecognizer.getPositionalQueryParameters();
-			this.namedParameters = parameterRecognizer.getNamedQueryParameters();
+			this.parameterList = toSmallList( parameterRecognizer.getParameterList() );
+			this.positionalParameters = toSmallMap( parameterRecognizer.getPositionalQueryParameters() );
+			this.namedParameters = toSmallMap( parameterRecognizer.getNamedQueryParameters() );
 		}
 
 		@Override

hibernate-core/src/main/java/org/hibernate/query/sql/internal/ParameterRecognizerImpl.java

@@ -7,7 +7,6 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 
 import org.hibernate.QueryException;
@@ -36,7 +35,7 @@ private enum ParameterStyle {
 
 	private int ordinalParameterImplicitPosition;
 
-	private List<ParameterOccurrence> parameterList;
+	private ArrayList<ParameterOccurrence> parameterList;
 	private final StringBuilder sqlStringBuffer = new StringBuilder();
 
 	public ParameterRecognizerImpl() {
@@ -81,7 +80,7 @@ public Map<Integer, QueryParameterImplementor<?>> getPositionalQueryParameters()
 		return positionalQueryParameters;
 	}
 
-	public List<ParameterOccurrence> getParameterList() {
+	public ArrayList<ParameterOccurrence> getParameterList() {
 		return parameterList;
 	}