[jira] [Commented] (OAK-4015) Expedite commits from the compactor

["Michael Dürig (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-4015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15148580#comment-15148580 ] 

Michael Dürig commented on OAK-4015:
------------------------------------

Initial implementation of an expeditable lock: https://github.com/mduerig/jackrabbit-oak/commit/8b9c9e598a60af14fe5fe791ff0dbe2fe646892c

In a quick test this brought the wait time of the compactor down to 7s from 22s resulting in a total of 6 vs. 16 extra compaction cycles. (The test went through 9 revision gc's in total). 

While I still like to collect more evidence on the effect of this change, I'd also be happy about a review mainly of {{ExpeditableLock}}.

> Expedite commits from the compactor
> -----------------------------------
>
>                 Key: OAK-4015
>                 URL: https://issues.apache.org/jira/browse/OAK-4015
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segmentmk
>            Reporter: Michael Dürig
>              Labels: compaction, gc, perfomance
>             Fix For: 1.6
>
>
> Concurrent commits during compaction cause those to be re-compacted. Currently it seems that the compaction thread can end up waiting for some time to acquire the commit lock [1], which in turn causes more commits to pile up to be re-compacted. I think this could be improved by tweaking the lock such that the compactor could jump ahead of the queue. I.e. use a lock which can be acquired in expedited mode. 
> [1] SegmentNodeStore#commitSemaphore



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