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https://issues.apache.org/jira/browse/LUCENE-4661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13547367#comment-13547367
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wolfgang hoschek commented on LUCENE-4661:
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Might be good to experiment with Linux block device read-ahead settings
(/sbin/blockdev --setra) and ensure using a file system that does write behind
(e.g. ext4 or xfs). Larger buffer sizes typically allow for more concurrent seq
streams even on spindles.
> 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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