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https://issues.apache.org/jira/browse/LUCENE-5722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14015472#comment-14015472
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Uwe Schindler commented on LUCENE-5722:
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I will just add some more test to TestMultiMMap so it checks that the correct
instances are returned (using instanceof). I just want to be sure, the 2
factory methods are creating the right impl classes for every combination of
slices and master indexinputs.
> 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
>
>
> 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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