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Date: Thu, 25 Oct 2007 11:16:50 -0700 (PDT)
From: "Yonik Seeley (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-994) Change defaults in IndexWriter to
 maximize "out of the box" performance
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    [ https://issues.apache.org/jira/browse/LUCENE-994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12537678 ] 

Yonik Seeley commented on LUCENE-994:
-------------------------------------

Yes, I guess one could consider it a minor breakage.
maxBufferedDocs previously ensured that changes were flushed every "n" docs.  They were flushed in a visible way, and I don't recall anything saying that one shouldn't open a reader before the writer was closed.

> Change defaults in IndexWriter to maximize "out of the box" performance
> -----------------------------------------------------------------------
>
>                 Key: LUCENE-994
>                 URL: https://issues.apache.org/jira/browse/LUCENE-994
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.3
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.3
>
>         Attachments: LUCENE-994.patch, writerinfo.zip
>
>
> This is follow-through from LUCENE-845, LUCENE-847 and LUCENE-870;
> I'll commit this once those three are committed.
> Out of the box performance of IndexWriter is maximized when flushing
> by RAM instead of a fixed document count (the default today) because
> documents can vary greatly in size.
> Likewise, merging performance should be faster when merging by net
> segment size since, to minimize the net IO cost of merging segments
> over time, you want to merge segments of equal byte size.
> Finally, ConcurrentMergeScheduler improves indexing speed
> substantially (25% in a simple initial test in LUCENE-870) because it
> runs the merges in the backround and doesn't block
> add/update/deleteDocument calls.  Most machines have concurrency
> between CPU and IO and so it makes sense to default to this
> MergeScheduler.
> Note that these changes will break users of ParallelReader because the
> parallel indices will no longer have matching docIDs.  Such users need
> to switch IndexWriter back to flushing by doc count, and switch the
> MergePolicy back to LogDocMergePolicy.  It's likely also necessary to
> switch the MergeScheduler back to SerialMergeScheduler to ensure
> deterministic docID assignment.
> I think the combination of these three default changes, plus other
> performance improvements for indexing (LUCENE-966, LUCENE-843,
> LUCENE-963, LUCENE-969, LUCENE-871, etc.) should make for some sizable
> performance gains Lucene 2.3!

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