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From "Andrei Dulceanu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-7162) Race condition on revisions head between compaction and scheduler could result in skipped commit
Date Mon, 05 Feb 2018 11:23:00 GMT

    [ https://issues.apache.org/jira/browse/OAK-7162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16352269#comment-16352269
] 

Andrei Dulceanu commented on OAK-7162:
--------------------------------------

Backported to 1.8 branch at r1823155.

> Race condition on revisions head between compaction and scheduler could result in skipped
commit
> ------------------------------------------------------------------------------------------------
>
>                 Key: OAK-7162
>                 URL: https://issues.apache.org/jira/browse/OAK-7162
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: segment-tar
>    Affects Versions: 1.8.0
>            Reporter: Andrei Dulceanu
>            Assignee: Andrei Dulceanu
>            Priority: Blocker
>              Labels: scalability
>             Fix For: 1.9.0, 1.10, 1.8.2
>
>         Attachments: OAK-7162-02.patch, OAK-7162-03.patch, OAK-7162-test.patch, OAK-7162.patch
>
>
> There is a race condition on {{TarRevisions#head}} between a running compaction trying
to set the new head [0] and the scheduler doing the same after executing a specific commit
[1]. If the compaction thread is first, then the head assignment in the scheduler will fail
and not be re-attempted. 
> IMO, the simple if statement should be changed to a while loop in which the head is refreshed
and the commit is re-applied against the new head, before attempting again to set a new head
in {{TarRevisions}}. This is somehow similar to what we previously had [2], but without the
unneeded optimistic/pessimistic strategies involving tokens.
> [0] https://github.com/apache/jackrabbit-oak/blob/trunk/oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/FileStore.java#L764
> [1] https://github.com/apache/jackrabbit-oak/blob/trunk/oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/scheduler/LockBasedScheduler.java#L253
> [2] https://github.com/apache/jackrabbit-oak/blob/1.6/oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/SegmentNodeStore.java#L686



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