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https://issues.apache.org/jira/browse/LUCENE-5722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14015629#comment-14015629
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ASF subversion and git services commented on LUCENE-5722:
---------------------------------------------------------
Commit 1599278 from [~thetaphi] in branch 'dev/branches/branch_4x'
[ https://svn.apache.org/r1599278 ]
Merged revision(s) 1599276 from lucene/dev/trunk:
LUCENE-5722: Optimize ByteBufferIndexInput#seek() by specializing
implementations. This improves random access as used by docvalues codecs if
used with MMapDirectory.
> Speed up MMapDirectory.seek()
> -----------------------------
>
> Key: LUCENE-5722
> URL: https://issues.apache.org/jira/browse/LUCENE-5722
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/store
> Reporter: Robert Muir
> Fix For: 4.9, 5.0
>
> Attachments: LUCENE-5722-multiseek.patch, LUCENE-5722.patch,
> LUCENE-5722.patch, LUCENE-5722.patch, LUCENE-5722.patch, LUCENE-5722.patch,
> LUCENE-5722.patch
>
>
> For traditional lucene access which is mostly sequential, occasional
> advance(), I think this method gets drowned out in noise.
> But for access like docvalues, its important. Unfortunately seek() is complex
> today because of mapping multiple buffers.
> However, the very common case is that only one map is used for a given clone
> or slice.
> When there is the possibility to use only a single mapped buffer, we should
> instead take advantage of ByteBuffer.slice(), which will adjust the internal
> mmap address and remove the offset calculation. furthermore we don't need the
> shift/mask or even the negative check, as they are then all handled with the
> ByteBuffer api: seek is a one-liner (with try/catch of course to convert
> exceptions).
> This makes docvalues access 20% faster, I havent tested conjunctions or
> anyhting like that.
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