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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