[jira] [Created] (LUCENE-5722) Speed up MMapDirectory.seek()

["Robert Muir (JIRA)" <ji...@apache.org>]

Robert Muir created LUCENE-5722:
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             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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