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https://issues.apache.org/jira/browse/OAK-3330?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Dürig resolved OAK-3330.
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Resolution: Fixed
* {{Segment.readString()}} loads the segment even when the string is in the
string cache. Fixed at http://svn.apache.org/viewvc?rev=1708401&view=rev
* Use read/write lock in {{FileStore}} instead of synchronize:
http://svn.apache.org/viewvc?rev=1708402&view=rev
* Read from {{FileChannel}} instead of {{RandomAccessFile}} to reduce
concurrency: http://svn.apache.org/viewvc?rev=1708403&view=rev
With above changes I see an increase of just above 50% in write throughput with
{{SegmenCompactionIT}} and above parameters.
> FileStore lock contention with concurrent writers
> -------------------------------------------------
>
> Key: OAK-3330
> URL: https://issues.apache.org/jira/browse/OAK-3330
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: segmentmk
> Reporter: Michael Dürig
> Assignee: Michael Dürig
> Labels: compaction
> Fix For: 1.4
>
> Attachments: OAK-3330.patch
>
>
> Concurrently writing to the file store can lead to a sever lock contention in
> {{FileStore#readSegment}}. That method searches the current {{TarWriter}}
> instance for the segment once it could not be found in any of the
> {{TarReader}} instances. This is the point where synchronizes on the
> {{FileStore}} instance, which leads to the contention.
> The effect is only observable once the segment cache becomes full and reads
> actually need to go to the file store. Thus a possible improvement could be
> to pin segments from the current tar writer to the cache. Alternatively we
> could try to ease locking by employing read/write locks where possible.
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