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Date: Thu, 4 Nov 2010 16:58:42 -0400 (EDT)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Subject: [jira] Commented: (CASSANDRA-1470) use direct io for compaction
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    [ https://issues.apache.org/jira/browse/CASSANDRA-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12928349#action_12928349 ] 

Jonathan Ellis commented on CASSANDRA-1470:
-------------------------------------------

I think you could use Lucene's DirectIOLinuxIndexInput with only minor modifications.  It does alignment already as well as buffered seeks.  It extends DataInput which may be all we need, if not, extending it from RandomAccessFile (just throw NotImplementedException on the write methods, we don't care about those) should be easy.

It depends on Lucene's NativePosixUtil.open_direct but your fcntl approach should work fine as well.

> use direct io for compaction
> ----------------------------
>
>                 Key: CASSANDRA-1470
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1470
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Pavel Yaskevich
>             Fix For: 0.6.7, 0.7.1
>
>         Attachments: 1470-v2.txt, 1470.txt, CASSANDRA-1470-for-0.6.patch, CASSANDRA-1470-v2.patch, CASSANDRA-1470-v3-0.7-with-LastErrorException-support.patch, CASSANDRA-1470.patch, use.DirectIORandomAccessFile.for.commitlog.against.1022235.patch
>
>
> When compaction scans through a group of sstables, it forces the data in the os buffer cache being used for hot reads, which can have a dramatic negative effect on performance.

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