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From "Jason Rutherglen (JIRA)" <>
Subject [jira] Updated: (LUCENE-2680) Improve how IndexWriter flushes deletes against existing segments
Date Wed, 03 Nov 2010 01:22:24 GMT


Jason Rutherglen updated LUCENE-2680:

    Attachment: LUCENE-2680.patch

Here's a new patch with properly working last segment index.  

The trunk version of apply deletes has become applyDeletesAll and is functionally unchanged.

There's a new method, DW applyDeletesToSegments called by _mergeInit for segments that are
about to be merged.  The deleted terms and queries for these segments are kept in hash sets
because docid-uptos are not needed.  

Like the last patch DW maintains the last segment index.  There's no need to maintain the
last-segindex per BD, instead I think it's only useful per DW, and for trunk we only have
one DW being used at a time.  

On successful merge, the last segment index is set to the segment index previous to the start
segment of the merge.  The merged segments deletes are coalesced into the startIndex-1's segment

> 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
> 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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