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From "Jason Rutherglen (JIRA)" <j...@apache.org>
Subject [jira] Updated: (LUCENE-2680) Improve how IndexWriter flushes deletes against existing segments
Date Mon, 22 Nov 2010 00:21:14 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-2680?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jason Rutherglen updated LUCENE-2680:
-------------------------------------

    Attachment: LUCENE-2680.patch

In trying to implement the per-segment deletes I encountered this error
from TestStressIndexing2. So I started over with a new checkout of trunk,
and started slowly adding in the per-segment code, running
TestStressIndexing2 as each part was added. The attached patch breaks,
though the deletes are still using the old code. There's clearly some kind
of synchronization issue, though nothing esoteric has been added, yikes.

{code}
[junit] Testcase: testMultiConfigMany(org.apache.lucene.index.TestStressIndexing2):	FAILED
    [junit] expected:<20> but was:<19>
    [junit] junit.framework.AssertionFailedError: expected:<20> but was:<19>
{code}

> Improve how IndexWriter flushes deletes against existing segments
> -----------------------------------------------------------------
>
>                 Key: LUCENE-2680
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2680
>             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,
LUCENE-2680.patch, LUCENE-2680.patch, 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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