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Date: Fri, 22 Aug 2008 15:02:44 -0700 (PDT)
From: "Matthew Mastracci (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-753) Use NIO positional read to avoid
 synchronization in FSIndexInput
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    [ https://issues.apache.org/jira/browse/LUCENE-753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624988#action_12624988 ] 

Matthew Mastracci commented on LUCENE-753:
------------------------------------------

This exception popped up out of the blue a few hours in.  No exceptions before it.  I'll see if I can figure out whether it was caused by our index snapshotting or if it's a bug elsewhere in NIOFSDirectory.

I haven't seen any exceptions like this with MMapDirectory, but it's possible there's something that we're doing that isn't correct.

{noformat} 
Caused by: java.nio.channels.ClosedChannelException
	at sun.nio.ch.FileChannelImpl.ensureOpen(FileChannelImpl.java:91)
	at sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:616)
	at com.dotspots.analyzer.index.NIOFSDirectory$NIOFSIndexInput.read(NIOFSDirectory.java:186)
	at com.dotspots.analyzer.index.NIOFSDirectory$NIOFSIndexInput.refill(NIOFSDirectory.java:218)
	at com.dotspots.analyzer.index.NIOFSDirectory$NIOFSIndexInput.readByte(NIOFSDirectory.java:232)
	at org.apache.lucene.store.IndexInput.readVInt(IndexInput.java:76)
	at org.apache.lucene.index.TermBuffer.read(TermBuffer.java:63)
	at org.apache.lucene.index.SegmentTermEnum.next(SegmentTermEnum.java:123)
	at org.apache.lucene.index.SegmentTermEnum.scanTo(SegmentTermEnum.java:154)
	at org.apache.lucene.index.TermInfosReader.scanEnum(TermInfosReader.java:223)
	at org.apache.lucene.index.TermInfosReader.get(TermInfosReader.java:217)
	at org.apache.lucene.index.SegmentReader.docFreq(SegmentReader.java:678)
	at org.apache.lucene.index.MultiSegmentReader.docFreq(MultiSegmentReader.java:373)
	at org.apache.lucene.index.MultiReader.docFreq(MultiReader.java:310)
	at org.apache.lucene.search.IndexSearcher.docFreq(IndexSearcher.java:87)
	at org.apache.lucene.search.Searcher.docFreqs(Searcher.java:178)
{noformat} 

> 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
>            Assignee: Michael McCandless
>             Fix For: 2.4
>
>         Attachments: FileReadTest.java, FileReadTest.java, FileReadTest.java, FileReadTest.java, FileReadTest.java, FileReadTest.java, FileReadTest.java, FSDirectoryPool.patch, FSIndexInput.patch, FSIndexInput.patch, LUCENE-753.patch, lucene-753.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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