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

[Steve Ebersole (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_28821 ] 

Steve Ebersole commented on HHH-2645:
-------------------------------------

1) I don't see where anyone is saying that using HashMap is the problem.  In fact the current Hibernate code is not even using HashMap, if you actually take a look.  In fact most comments are explicitly pointing to the use of synchronization as the cause.  And that probably is the case; call me pragmatic, I just prefer hard numbers.

2) This should be a *unit test* of the specific map usage pattern.  We already have enough integration tests that dont cover enough low-level details like this.  We need to start scaling out the test suite to contain both more unit tests and more load/perf tests.

3) Where did these numbers come from?  I assume this is because you are discussing integration tests and it took that long for you to get proper concurrent load on the Map structure.  This is another reason to have unit tests for this as well.

> 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
>
>
> 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)
>  

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