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List:       lucene-dev
Subject:    [jira] [Created] (LUCENE-5722) Speed up MMapDirectory.seek()
From:       "Robert Muir (JIRA)" <jira () apache ! org>
Date:       2014-05-31 6:17:01
Message-ID: JIRA.12717713.1401516916062.52801.1401517021717 () arcas
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Robert Muir created LUCENE-5722:
-----------------------------------

             Summary: 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


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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