HHH-15100 Limitation of metamodel imports cache causes severe performance drops in large projects

hibernate-core/src/main/java/org/hibernate/metamodel/model/domain/internal/JpaMetamodelImpl.java

@@ -70,7 +70,6 @@ import org.hibernate.type.spi.TypeConfiguration;
  */
 public class JpaMetamodelImpl implements JpaMetamodelImplementor, Serializable {
 	private static final EntityManagerMessageLogger log = HEMLogging.messageLogger( JpaMetamodel.class );
-	private static final ImportInfo<?> INVALID_IMPORT = new ImportInfo<>( null, null );
 
 	private static class ImportInfo<T> {
 		final String importedName;
@@ -98,6 +97,7 @@ public class JpaMetamodelImpl implements JpaMetamodelImplementor, Serializable {
 	private final Map<Class<?>, String> entityProxyInterfaceMap = new HashMap<>();
 
 	private final Map<String, ImportInfo<?>> nameToImportMap = new ConcurrentHashMap<>();
+	private final Map<String,Object> knownInvalidnameToImportMap = new ConcurrentHashMap<>();
 
 
 	public JpaMetamodelImpl(TypeConfiguration typeConfiguration, JpaCompliance jpaCompliance) {
@@ -281,9 +281,15 @@ public class JpaMetamodelImpl implements JpaMetamodelImplementor, Serializable {
 
 	private <T> ImportInfo<T> resolveImport(final String name) {
 		final ImportInfo<?> importInfo = nameToImportMap.get( name );
+		//optimal path first
 		if ( importInfo != null ) {
 			//noinspection unchecked
-			return importInfo == INVALID_IMPORT ? null : (ImportInfo<T>) importInfo;
+			return (ImportInfo<T>) importInfo;
+		}
+		else {
+			//then check the negative cache, to avoid bothering the classloader unnecessarily
+			if ( knownInvalidnameToImportMap.containsKey( name ) ) {
+				return null;
 			}
 			else {
 				// see if the name is a fully-qualified class name
@@ -293,20 +299,27 @@ public class JpaMetamodelImpl implements JpaMetamodelImplementor, Serializable {
 					// note that ConcurrentHashMap does not support null value so a marker entry is needed
 					// [HHH-14948] But only add it if the cache size isn't getting too large, as in some use cases
 					// the queries are dynamically generated and this cache could lead to memory leaks when left unbounded.
-				if ( nameToImportMap.size() < 1_000 ) {
-					nameToImportMap.put( name, INVALID_IMPORT );
+					if ( knownInvalidnameToImportMap.size() < 1_000 ) {
+						//TODO this collection might benefit from a LRU eviction algorithm,
+						//we currently have no evidence for this need but this could be explored further.
+						//To consider that we don't have a hard dependency on a cache implementation providing LRU semantics.
+						//Alternatively - even better - would be to precompute all possible valid options and
+						//store them in nameToImportMap on bootstrap: if that can be filled with all (comprehensive)
+						//valid values, then there is no need for ever bothering the classloader.
+						knownInvalidnameToImportMap.put( name, name );
 					}
 					return null;
 				}
 				else {
 					// it is a fully-qualified class name - add it to the cache
-				//		so we do not keep trying later
+					// so to not needing to load from the classloader again
 					final ImportInfo<T> info = new ImportInfo<>( name, loadedClass );
 					nameToImportMap.put( name, info );
 					return info;
 				}
 			}
 		}
+	}
 
 	@SuppressWarnings("unchecked")
 	private void applyNamedEntityGraphs(Collection<NamedEntityGraphDefinition> namedEntityGraphs) {

hibernate-core/src/test/java/org/hibernate/orm/test/hql/MetamodelBoundedCacheTest.java

@@ -38,15 +38,22 @@ public class MetamodelBoundedCacheTest extends BaseNonConfigCoreFunctionalTestCa
 			jpaMetamodel.qualifyImportableName( "nonexistend" + i );
 		}
 
-		Field field = JpaMetamodelImpl.class.getDeclaredField( "nameToImportMap" );
-		field.setAccessible( true );
+		Map<?, ?> validImports = extractMapFromMetamodel( jpaMetamodel, "nameToImportMap" );
+		Map<?, ?> invalidImports  = extractMapFromMetamodel( jpaMetamodel, "knownInvalidnameToImportMap" );
 
-		//noinspection unchecked
-		Map<String, String> imports = (Map<String, String>) field.get( jpaMetamodel );
+		assertEquals( 2, validImports.size() );
 
 		// VERY hard-coded, but considering the possibility of a regression of a memory-related issue,
 		// it should be worth it
-		assertEquals( 1000, imports.size() );
+		assertEquals( 1000, invalidImports.size() );
+	}
+
+
+	private Map<?, ?> extractMapFromMetamodel(final JpaMetamodel jpaMetamodel, final String fieldName) throws NoSuchFieldException, IllegalAccessException {
+		Field field = JpaMetamodelImpl.class.getDeclaredField( fieldName );
+		field.setAccessible( true );
+		//noinspection unchecked
+		return (Map<?,?>) field.get( jpaMetamodel );
 	}
 
 	@Override