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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1470) use direct io for compaction
Date Thu, 04 Nov 2010 20:58:42 GMT

    [ 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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