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https://issues.apache.org/jira/browse/LUCENE-2814?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael McCandless resolved LUCENE-2814.
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Resolution: Fixed
Fix Version/s: 4.0
3.1
> stop writing shared doc stores across segments
> ----------------------------------------------
>
> Key: LUCENE-2814
> URL: https://issues.apache.org/jira/browse/LUCENE-2814
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Affects Versions: 3.1, 4.0
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 3.1, 4.0
>
> Attachments: LUCENE-2814.patch, LUCENE-2814.patch, LUCENE-2814.patch,
> LUCENE-2814.patch, LUCENE-2814.patch
>
>
> Shared doc stores enables the files for stored fields and term vectors to be
> shared across multiple segments. We've had this optimization since 2.1 I
> think.
> It works best against a new index, where you open an IW, add lots of docs,
> and then close it. In that case all of the written segments will reference
> slices a single shared doc store segment.
> This was a good optimization because it means we never need to merge these
> files. But, when you open another IW on that index, it writes a new set of
> doc stores, and then whenever merges take place across doc stores, they must
> now be merged.
> However, since we switched to shared doc stores, there have been two
> optimizations for merging the stores. First, we now bulk-copy the bytes in
> these files if the field name/number assignment is "congruent". Second, we
> now force congruent field name/number mapping in IndexWriter. This means
> this optimization is much less potent than it used to be.
> Furthermore, the optimization adds *a lot* of hair to
> IndexWriter/DocumentsWriter; this has been the source of sneaky bugs over
> time, and causes odd behavior like a merge possibly forcing a flush when it
> starts. Finally, with DWPT (LUCENE-2324), which gets us truly concurrent
> flushing, we can no longer share doc stores.
> So, I think we should turn off the write-side of shared doc stores to pave
> the path for DWPT to land on trunk and simplify IW/DW. We still must support
> reading them (until 5.0), but the read side is far less hairy.
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