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https://issues.apache.org/jira/browse/LUCENE-2816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12972420#action_12972420
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Michael McCandless commented on LUCENE-2816:
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Good grief! What amazing gains, especially w/ PFor codec which of course makes
super heavy use of .readInt(). Awesome Robert!
This will mean w/ the cutover to FORPFOR codec for 4.0, MMapDir will likely
have a huge edge over NIOFSDir?
> MMapDirectory speedups
> ----------------------
>
> Key: LUCENE-2816
> URL: https://issues.apache.org/jira/browse/LUCENE-2816
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Store
> Affects Versions: 3.1, 4.0
> Reporter: Robert Muir
> Assignee: Robert Muir
> Attachments: LUCENE-2816.patch
>
>
> MMapDirectory has some performance problems:
> # When the file is larger than Integer.MAX_VALUE, we use MultiMMapIndexInput,
> which does a lot of unnecessary bounds-checks for its buffer-switching etc.
> Instead, like MMapIndexInput, it should rely upon the contract of these
> operations
> in ByteBuffer (which will do a bounds check always and throw
> BufferUnderflowException).
> Our 'buffer' is so large (Integer.MAX_VALUE) that its rare this happens and
> doing
> our own bounds checks just slows things down.
> # the readInt()/readLong()/readShort() are slow and should just defer to
> ByteBuffer.readInt(), etc
> This isn't very important since we don't much use these, but I think there's
> no reason
> users (e.g. codec writers) should have to readBytes() + wrap as bytebuffer +
> get an
> IntBuffer view when readInt() can be almost as fast...
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