[jira] [Commented] (OAK-3330) FileStore lock contention with concurrent writers

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

    [ https://issues.apache.org/jira/browse/OAK-3330?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14726900#comment-14726900 ] 

Michael Dürig commented on OAK-3330:
------------------------------------

Note that his also impacts compaction as this is just another thread writing to the repository. 

> 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
>
> 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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