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https://issues.apache.org/jira/browse/JCR-2699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12907656#action_12907656
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Jukka Zitting commented on JCR-2699:
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Based on some profiling and other analysis based on the concurrent read
performance tests I added, here's a few pointers for potential improvements:
* The bundle cache is hidden behind the synchronization layer of the bundle
persistence classes, which causes a single cache miss to block access to the
entire cache while the missing bundle is fetched from disk. We should revise
the synchronization level to allow the bundle cache to serve concurrent
requests even when the persistence manager is busy waiting for I/O.
* The synchronization overhead in DefaultISMLocking was pretty high. I was
seeing some significant time spent there even though in a concurrent read test
a thread should never get blocked by the ISMLocking implementation. I
refactored the DefaultISMLocking class in revision 995411 for issue JCR-2089,
which solved most of this problem. I didn't try it yet, but I suspect that the
FineGrainedISMLocking class may be even worse in this regard.
* Path handling code shows up quite a bit (2-5% of active CPU time) in
profiling results. We should be able to avoid that overhead as described in the
follow-up issue JCR-2744.
* The synchronized cache blocks in ItemManager and SharedItemStateManager show
up as contention bottlenecks in highly concurrent read scenarios.
* Access control checks with the DefaultAccessManager add significant amount of
overhead when compared to the dummy SimpleAccessManager implementation. Even
though ACL optimizations are somewhat orthogonal to concurrency improvements,
the large number of usually very fine-grained content accesses done by the
DefaultAccessManager puts significant extra pressure on the above-mentioned
contention points, so we should see notable concurrency improvements also from
optimized ACL evaluation.
> Improve read/write concurrency
> ------------------------------
>
> Key: JCR-2699
> URL: https://issues.apache.org/jira/browse/JCR-2699
> Project: Jackrabbit Content Repository
> Issue Type: Improvement
> Components: jackrabbit-core
> Reporter: Jukka Zitting
> Assignee: Jukka Zitting
> Attachments: ConcurrentReadTest.png
>
>
> I'd like to set up a few performance tests to help identify our worst
> bottlenecks for various kinds of concurrent read-only and read-write access
> patterns.
> Once identified, I'm hoping to fix at least some of those bottlenecks.
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