[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2645) Synchronization bottleneck in EntityModeToTuplizerMapping

From my numbers, the JDK ConcurrentHashMap is clearly the best option, but unfortunately not available as a solution until 4.0 when we move to jdk5. Other than that, the Doug Lea / Oswego ConcurrentReaderHashMap seemed to significantly beat the others for this access pattern.

Synchronization bottleneck in EntityModeToTuplizerMapping --------------------------------------------------------- Key: HHH-2645 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2645 Project: Hibernate3 Issue Type: Patch Components: core Affects Versions: 3.2.3, 3.2.4, 3.2.4.sp1 Environment: Hibernate 3.2.3 (and later), Sun's JDK 1.4.2_12 (server VM) on SunOS 5.10, Oracle 10g R2 Reporter: Erik Bergersjö Assignee: Gail Badner Priority: Minor Attachments: concurrentreader.patch, maptest.patch We have had a major performance bottleneck in EntityModeToTuplizerMapping with Hibernate version 3.2.3 and the code for that class in 3.2.4sp1 is unchanged. We have found a solution that solves the issue and would like to get it into the real version. I submitted to the user forum first and was asked to create a JIRA issue. The problematic line is: private final Map tuplizers = Collections.synchronizedMap( new SequencedHashMap() ); We have changed it to (using util.concurrent): private final Map tuplizers = new EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap(); This change alone makes our use cases six times faster. The difference is that ConcurrentReaderHashMap handles concurrent readers much better, they don't have to wait for each other. The problem occurs when a high number of threads try to initialize sets (see mapping below). A thread dump showed a high number of threads waiting for the same monitor, see partial stack trace below. The code runs on Sun's JDK 1.4.2_12 (server VM) on SunOS 5.10 and the kernel spends a lot of time handling mutexes with the original implementation. That time disappears from the radar screen with the fixed version. Example mapping for set: [code] <set name="lines" lazy="true" inverse="true" cascade="all-delete-orphan"> <key> <column name="col1" not-null="true" /> <column name="col2" not-null="true" /> </key> <one-to-many class="LineClass" /> </set> [/code] Stack trace (partial): "Thread-108" prio=5 tid=0x05852e90 nid=0x103 waiting for monitor entry [0x3ed7e000..0x3ed7fc28] at java.util.Collections$SynchronizedMap.get(Collections.java:1942) - waiting to lock <0x89d30788> (a java.util.Collections$SynchronizedMap) at org.hibernate.tuple.EntityModeToTuplizerMapping.getTuplizerOrNull(EntityModeToTuplizerMapping.java:53) at org.hibernate.tuple.EntityModeToTuplizerMapping.getTuplizer(EntityModeToTuplizerMapping.java:66) at org.hibernate.type.ComponentType.getPropertyValues(ComponentType.java:353) at org.hibernate.type.ComponentType.isEqual(ComponentType.java:141) at org.hibernate.engine.CollectionKey.equals(CollectionKey.java:50) at java.util.HashMap.eq(HashMap.java:274) at java.util.HashMap.get(HashMap.java:323) at org.hibernate.engine.loading.CollectionLoadContext.getLocalLoadingCollectionEntry(CollectionLoadContext.java:163) at org.hibernate.engine.loading.CollectionLoadContext.locateLoadingCollectionEntry(CollectionLoadContext.java:150) at org.hibernate.engine.loading.CollectionLoadContext.getLoadingCollection(CollectionLoadContext.java:92) at org.hibernate.loader.Loader.readCollectionElement(Loader.java:1003) at org.hibernate.loader.Loader.readCollectionElements(Loader.java:646) at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:591) at org.hibernate.loader.Loader.doQuery(Loader.java:701) at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236) at org.hibernate.loader.Loader.loadCollection(Loader.java:1994) at org.hibernate.loader.collection.CollectionLoader.initialize(CollectionLoader.java:36) at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:565) at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:60) at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1716) at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:344) at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:86) at org.hibernate.collection.PersistentSet.iterator(PersistentSet.java:163)