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From "Jason Rutherglen (JIRA)" <>
Subject [jira] Commented: (LUCENE-2680) Improve how IndexWriter flushes deletes against existing segments
Date Sat, 06 Nov 2010 21:59:22 GMT


Jason Rutherglen commented on LUCENE-2680:

Pushing the segment infos seems to have cleared up some of the tests failing, however intermittently
(1/4 of the time) there's the one below.

I'm going to re-add lastSegmentInfo/Index, and assert that if we're not using it, that the
deletes obtained from the segmentinfo -> deletes map is the same.  

[junit] Testsuite: org.apache.lucene.index.TestStressIndexing2
    [junit] Testcase: testRandom(org.apache.lucene.index.TestStressIndexing2):	FAILED
    [junit] expected:<12> but was:<11>
    [junit] junit.framework.AssertionFailedError: expected:<12> but was:<11>
    [junit] 	at org.apache.lucene.util.LuceneTestCase$LuceneTestCaseRunner.runChild(
    [junit] 	at org.apache.lucene.util.LuceneTestCase$LuceneTestCaseRunner.runChild(
    [junit] 	at org.apache.lucene.index.TestStressIndexing2.verifyEquals(
    [junit] 	at org.apache.lucene.index.TestStressIndexing2.verifyEquals(
    [junit] 	at org.apache.lucene.index.TestStressIndexing2.testRandom(

> Improve how IndexWriter flushes deletes against existing segments
> -----------------------------------------------------------------
>                 Key: LUCENE-2680
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>             Fix For: 4.0
>         Attachments: LUCENE-2680.patch, LUCENE-2680.patch, LUCENE-2680.patch, LUCENE-2680.patch
> IndexWriter buffers up all deletes (by Term and Query) and only
> applies them if 1) commit or NRT getReader() is called, or 2) a merge
> is about to kickoff.
> We do this because, for a large index, it's very costly to open a
> SegmentReader for every segment in the index.  So we defer as long as
> we can.  We do it just before merge so that the merge can eliminate
> the deleted docs.
> But, most merges are small, yet in a big index we apply deletes to all
> of the segments, which is really very wasteful.
> Instead, we should only apply the buffered deletes to the segments
> that are about to be merged, and keep the buffer around for the
> remaining segments.
> I think it's not so hard to do; we'd have to have generations of
> pending deletions, because the newly merged segment doesn't need the
> same buffered deletions applied again.  So every time a merge kicks
> off, we pinch off the current set of buffered deletions, open a new
> set (the next generation), and record which segment was created as of
> which generation.
> This should be a very sizable gain for large indices that mix
> deletes, though, less so in flex since opening the terms index is much
> faster.

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