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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-5310) Merge Threads unnecessarily block on SerialMergeScheduler
Date Sun, 27 Apr 2014 15:38:15 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-5310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13982360#comment-13982360
] 

Robert Muir commented on LUCENE-5310:
-------------------------------------

{quote}
I also think CMS can deadlock (stall all merges) if you ever try to
decrease the maxMergeCount when too many merges were already running,
because the stall logic would get to a point where no thread would
ever be allowed to unstall. So I changed it (and MergeScheduler) to
require the maxMergeCount up front.
{quote}

I proposed this on LUCENE-5310 a while back, but it didnt take then.

> Merge Threads unnecessarily block on SerialMergeScheduler
> ---------------------------------------------------------
>
>                 Key: LUCENE-5310
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5310
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/index
>    Affects Versions: 4.5, 5.0
>            Reporter: Simon Willnauer
>            Priority: Minor
>             Fix For: 4.9, 5.0
>
>         Attachments: LUCENE-5310.patch, LUCENE-5310.patch, LUCENE-5310.patch, LUCENE-5310.patch,
LUCENE-5310.patch, LUCENE-5310.patch
>
>
> I have been working on a high level merge multiplexer that shares threads across different
IW instances and I came across the fact that SerialMergeScheduler actually blocks incoming
thread is a merge in going on. Yet this blocks threads unnecessarily since we pull the merges
in a loop anyway. We should use a tryLock operation instead of syncing the entire method?



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