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https://issues.apache.org/jira/browse/LUCENE-2816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12972413#action_12972413
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Uwe Schindler commented on LUCENE-2816:
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Awesome, Ro bert is changing to the MMap Performance Policeman!
I like the idea to simply delegate the methods and catch exception to fallback
to manual read with boundary transition! I just wanted to be sure that the
position pointer in the buffer does not partly go forward when you read request
fails at a buffer boundary, but that seems to be the case.
> 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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