[jira] Commented: (CASSANDRA-1470) use direct io for compaction

["Robert Coli (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920714#action_12920714 ] 

Robert Coli commented on CASSANDRA-1470:
----------------------------------------

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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