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From Michael Dürig (JIRA) <j...@apache.org>
Subject [jira] [Resolved] (OAK-3055) Improve segment cache in SegmentTracker
Date Wed, 15 Jul 2015 14:10:05 GMT

     [ https://issues.apache.org/jira/browse/OAK-3055?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael Dürig resolved OAK-3055.
--------------------------------
       Resolution: Fixed
    Fix Version/s:     (was: 1.3.5)
                   1.3.3

Replaced the segment cache with a LIRS implementation at http://svn.apache.org/r1691219. In
addition http://svn.apache.org/r1691220 exposes the {{CacheStatsMBean}} for this new cache.


I can confirm that this in conjunction with OAK-3007 considerably reduces the observer lock
contention.


> Improve segment cache in SegmentTracker
> ---------------------------------------
>
>                 Key: OAK-3055
>                 URL: https://issues.apache.org/jira/browse/OAK-3055
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segmentmk
>            Reporter: Michael Dürig
>            Assignee: Michael Dürig
>              Labels: resilience, scalability
>             Fix For: 1.3.3
>
>         Attachments: OAK-3055.patch
>
>
> The hand crafted segment cache in {{SegmentTracker}} is prone to lock contentions in
concurrent access scenarios. As {{SegmentNodeStore#merge}} might also end up acquiring this
lock while holding the commit semaphore the situation can easily lead to many threads being
blocked on the commit semaphore. The {{SegmentTracker}} cache doesn't differentiate between
read and write access, which means that reader threads can block writer threads. 



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