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List:       lucene-dev
Subject:    [jira] Commented: (LUCENE-753) Use NIO positional read to avoid
From:       "Brian Pinkerton (JIRA)" <jira () apache ! org>
Date:       2008-06-30 23:30:46
Message-ID: 211803434.1214868646590.JavaMail.jira () brutus
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    [ https://issues.apache.org/jira/browse/LUCENE-753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12609401#action_12609401 \
] 

Brian Pinkerton commented on LUCENE-753:
----------------------------------------

I was curious about the discrepancy between the ChannelPread implementation and the \
SeparateFile implementation that Yonik saw.  At least on Mac OS X, the kernel \
implementation of read is virtually the same as pread, so there shouldn't be any \
appreciable performance difference unless the VM is doing something funny.  Sure \
enough, the implementations of read() under RandomAccessFile and read() under \
FileChannel are totally different.  The former relies on either a buffer allocated \
either on the stack or by malloc, while the latter allocates a native buffer and \
copies the results to the original array.

Switching to a native buffer in the benchmark yields identical results for \
ChannelPread and SeparateFile on 1.5 and 1.6 on OS X.  I'm attaching an \
implementation of ChannelPreadDirect that uses a native buffer.

This may be a moot point because any implementation inside Lucene needs to consume a \
byte[] and not a ByteBuffer, but at least it's informative.



> Use NIO positional read to avoid synchronization in FSIndexInput
> ----------------------------------------------------------------
> 
> Key: LUCENE-753
> URL: https://issues.apache.org/jira/browse/LUCENE-753
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Store
> Reporter: Yonik Seeley
> Attachments: FileReadTest.java, FileReadTest.java, FileReadTest.java, \
> FileReadTest.java, FileReadTest.java, FileReadTest.java, FSIndexInput.patch, \
> FSIndexInput.patch, lucene-753.patch 
> 
> As suggested by Doug, we could use NIO pread to avoid synchronization on the \
> underlying file. This could mitigate any MT performance drop caused by reducing the \
> number of files in the index format.

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