[jira] [Comment Edited] (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=15326951#comment-15326951 ] 

Michael Dürig edited comment on OAK-4015 at 6/13/16 8:09 AM:
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Not sure whether this is a good idea any more. The commit scheduler is a concern of the higher level {{SegmentNodeStore}}. Accessing it directly from the {{FileStore}} would break encapsulation. We should probably stick with a lock based implementation as proposed here. 

After all the refactorings of the past weeks the attached patch is void though: compactor related commits are now directly applied at {{FileStore}} level and do not involve the {{SegmentNodeStore}} any more. What we still can do is to come up with a locking strategy in {{TarRevisions}} that prefers the compactor. That is, the lock should not allow a new reader any more once a writer wants to enter the lock. The {{ReentrantReadWriteLock}}, which is currently used does most likely not behave like this. 


was (Author: mduerig):
Not sure whether this is a good idea any more. The commit scheduler is a concern of the higher level {{SegmentNodeStore}}. Accessing it directly from the {{FileStore}} would break encapsulation. We should probably stick with a lock based implementation as proposed here. 

> Expedite commits from the compactor
> -----------------------------------
>
>                 Key: OAK-4015
>                 URL: https://issues.apache.org/jira/browse/OAK-4015
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segment-tar
>            Reporter: Michael Dürig
>              Labels: compaction, gc, perfomance
>             Fix For: 1.6
>
>         Attachments: OAK-4015-histo.png, OAK-4015-wait-time.png
>
>
> 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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