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From "Markus Jelsma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4661) Reduce default maxMerge/ThreadCount for ConcurrentMergeScheduler
Date Tue, 08 Jan 2013 15:16:13 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13546937#comment-13546937
] 

Markus Jelsma commented on LUCENE-4661:
---------------------------------------

Thanks. Hope to do some experiments. Will report back if i can finish it up.
                
> Reduce default maxMerge/ThreadCount for ConcurrentMergeScheduler
> ----------------------------------------------------------------
>
>                 Key: LUCENE-4661
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4661
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 4.1, 5.0
>
>
> I think our current defaults (maxThreadCount=#cores/2,
> maxMergeCount=maxThreadCount+2) are too high ... I've frequently found
> merges falling behind and then slowing each other down when I index on
> a spinning-magnets drive.
> As a test, I indexed all of English Wikipedia with term-vectors (=
> heavy on merging), using 6 threads ... at the defaults
> (maxThreadCount=3, maxMergeCount=5, for my machine) it took 5288 sec
> to index & wait for merges & commit.  When I changed to
> maxThreadCount=1, maxMergeCount=2, indexing time sped up to 2902
> seconds (45% faster).  This is on a spinning-magnets disk... basically
> spinning-magnets disk don't handle the concurrent IO well.
> Then I tested an OCZ Vertex 3 SSD: at the current defaults it took
> 1494 seconds and at maxThreadCount=1, maxMergeCount=2 it took 1795 sec
> (20% slower).  Net/net the SSD can handle merge concurrency just fine.
> I think we should change the defaults: spinning magnet drives are hurt
> by the current defaults more than SSDs are helped ... apps that know
> their IO system is fast can always increase the merge concurrency.

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