Robert Muir created LUCENE-5729:
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Summary: explore random-access methods to IndexInput
Key: LUCENE-5729
URL: https://issues.apache.org/jira/browse/LUCENE-5729
Project: Lucene - Core
Issue Type: Improvement
Reporter: Robert Muir
Traditionally lucene access is mostly reading lists of postings and geared at
that, but for random-access stuff like docvalues, it just creates overhead.
So today we are hacking around it, by doing this random access with
seek+readXXX, but this is inefficient (additional checks by the jdk that we
dont need).
As a hack, I added the following to IndexInput, changed direct packed ints
decode to use them, and implemented in MMapDir:
{code}
byte readByte(long pos) --> ByteBuffer.get(pos)
short readShort(long pos) --> ByteBuffer.getShort(pos)
int readInt(long pos) --> ByteBuffer.getInt(pos)
long readLong(long pos) --> ByteBuffer.getLong(pos)
{code}
This gives ~30% performance improvement for docvalues (numerics, sorting
strings, etc)
We should do a few things first before working this (LUCENE-5728: use slice api
in decode, pad packed ints so we only have one i/o call ever, etc etc) but I
think we need to figure out such an API.
It could either be on indexinput like my hack (this is similar to ByteBuffer
API with both relative and absolute methods), or we could have a separate API.
But i guess arguably IOContext exists to supply hints too, so I dont know which
is the way to go.
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