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From "Martijn Hendriks (JIRA)" <j...@apache.org>
Subject [jira] Created: (JCR-731) Can the caching mechanism be improved?
Date Fri, 02 Feb 2007 14:42:05 GMT
Can the caching mechanism be improved?

                 Key: JCR-731
                 URL: https://issues.apache.org/jira/browse/JCR-731
             Project: Jackrabbit
          Issue Type: Improvement
            Reporter: Martijn Hendriks

Hi all,

We've identified the method "getNonVirtualItemState" in the SharedItemStateManager as a hot
spot in our application. To avoid the contention in "getNonVirtualItemState", we have pulled
the isCached call out of the synchronized block and re-implemented the MLRUItemStateCache.
It uses a HashMap that contains the ItemId-ItemState mapping and a ReadWriteLock to replace
all synchronized blocks in the code. The implementation of "shrinkIfRequired" unfortunatly
got much more expensive as the entryset of the HashMap must be sorted by accesscount. This
method then clearly is a bottleneck. We solved this by changing the CacheManager a bit: the
"resizeAll" method avoids the eviction of items out of caches as long as possible.

These changes work out really well for our application. I have attached the changed files;
comments/feedback are very welcome!


Martijn Hendriks
<GX> creative online development B.V.
t: 024 - 3888 261
f: 024 - 3888 621
e: martijnh@gx.nl
Wijchenseweg 111
6538 SW Nijmegen

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