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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-5722) Speed up MMapDirectory.seek()
Date Sun, 01 Jun 2014 11:17:02 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-5722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14014957#comment-14014957
] 

Robert Muir commented on LUCENE-5722:
-------------------------------------

As far as the second idea, of course that's something nice to look into. But I don't think
it will ever be simpler than the one buffer case.

> Speed up MMapDirectory.seek()
> -----------------------------
>
>                 Key: LUCENE-5722
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5722
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Robert Muir
>         Attachments: 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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