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https://issues.apache.org/jira/browse/CASSANDRA-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920714#action_12920714
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Robert Coli commented on CASSANDRA-1470:
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Was looking over this patch and noticed it only does O_DIRECT on SSTable
writes. The commit log contains 100% of writes, but only the header is ever
read except in the relatively rare replay case. It seems like it would be worth
doing these writes as O_DIRECT to avoid polluting the page cache with them,
spoke with Goffinet and he agreed. I looked at the code and it appears to be a
two line patch, which I've attached.
> 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
> Fix For: 0.6.7, 0.7.1
>
> Attachments: 1470-v2.txt, 1470.txt,
> 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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