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From "Jeremy Bauer (JIRA)" <>
Subject [jira] Updated: (OPENJPA-637) Significant performance degradation when data cache is enabled
Date Mon, 23 Jun 2008 19:36:44 GMT


Jeremy Bauer updated OPENJPA-637:

    Attachment: CacheImplTest.jar

I've attached a standalone test for running some tests using various cache implementations
and configurations.  It behaves similarly to the benchmark that exposed this problem.  The
test allows  configuration of number of threads, max data size, max cache size, whether external
locking is enabled, and the cache implementation type.

This test is showing similar results as to what I've previously posted; a write lock causing
contention when the cache becomes full.  When the external write lock (a reentrant lock over
and above internal cache locking) is enabled and the data size is ~5000 entries larger than
the max cache size performance drops significantly.  The external lock simulates the reentrant
lock used by DataCacheStoreManager to ensure the cache does not get updated with an old version
of data.

This test should provide a better idea of what I'm seeing.  Aside, there is an option to run
directly with java.util.concurrent.ConcurrentHashMap and it performs very well - although
there is no null masking or maximum size on the cache.  

To get a list of options:  java -cp CacheImplTest.jar;commons-collections-3.2.jar cachetest.Main

Patrick - What behavior/environment does your benchmark test?  Is it possible that your cache
size is very near the size of your data so you are not hitting the problem?

> Significant performance degradation when data cache is enabled
> --------------------------------------------------------------
>                 Key: OPENJPA-637
>                 URL:
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: datacache, lib
>    Affects Versions: 1.2.0
>            Reporter: Jeremy Bauer
>         Attachments: CacheImplTest.jar, OPENJPA-637.patch
> Performance testing is showing a severe data cache performance degradation when moving
from 1.0.x OpenJPA code to 1.2.0 level code.  Profiling showed the problem to be in the new
random eviction scheme which runs when the cache reaches its maximum number of entries.  This
code was changed significantly when OpenJPA moved to Java 5 java.util.concurrent.ConcurrentHashMap
and away from the OpenJPA implementation of ConcurrentHashMap.  A macro-benchmark showed a
20% performance degradation from base 1.2.0 code when the cache reaches its maximum size;
prompting eviction in order to add new cache entries.
> I've found that the new random eviction code appears to be improved in the very recent
666903 commit, but data cache performance remains considerably slower than the 1.0.x implementation.
 Profiles with the 666903 changes show test threads to be waiting on the reentrant write lock
in the CacheMap wrapper (which now wrappers a max size capable, null handling, subclass of
java.util.concurrent.ConcurrentHashMap).  Investigation is underway to determine whether the
write lock is necessary (ie. can java.util.conncurrentConcurrentHashMap manage the cache without
the need for external locking) and/or if changes could be made which would result in a significant
reduction in contention for the lock.  Any thoughts/ideas on that would be extremely helpful.
> Performance tests run with the 1.2.0 code base, using the OpenJPA version of ConcurrentHashMap
(instead of the Java 5 java.util.concurrent.ConcurrentHashMap-based implementation) have shown
that  performance of the data cache is significantly better when the legacy OpenJPA implementation
is used.  Based on the results, it appears that OpenJPA should be using the the legacy ConcurrentHashMap
instead of the Java 5-based implementation -- or the new Java 5-based implementation needs
to be improved considerably in order to perform as well as 1.0.x.
> I am opening this as a 1.2.0 issue, although it very likely affects 1.1.x as well.  Testing
has not been performed on 1.1.x to confirm the problem exists on that release.

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