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From "T Jake Luciani (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1470) use direct io for compaction
Date Thu, 16 Dec 2010 19:31:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12972178#action_12972178
] 

T Jake Luciani commented on CASSANDRA-1470:
-------------------------------------------

@Chris

I re-ran the benchmarks with and tracked context switching and TLB flushes. 
fadvise approach showed a ~11% increase TLB flushing and a ~11% decrease in context switching.
These number goes up and down depending on the value of BRAF.maxBytesInPageCache (currently
128mb)

Also keep in mind this benchmark only shows improvement of compaction of a CF currently not
in the page cache.  if a "hot" CF was compacted you would see no improvement since the pages
will be flushed once the old sstables are removed.  in another patch we can try to migrate
active pages as described in my comments above.

> 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: 0.7.1
>
>         Attachments: 1470-v2.txt, 1470.txt, CASSANDRA-1470-for-0.6.patch, CASSANDRA-1470-v10-for-0.7.patch,
CASSANDRA-1470-v11-for-0.7.patch, CASSANDRA-1470-v12-0.7.patch, CASSANDRA-1470-v13-0.7.patch,
CASSANDRA-1470-v14-0.7.patch, CASSANDRA-1470-v2.patch, CASSANDRA-1470-v3-0.7-with-LastErrorException-support.patch,
CASSANDRA-1470-v4-for-0.7.patch, CASSANDRA-1470-v5-for-0.7.patch, CASSANDRA-1470-v6-for-0.7.patch,
CASSANDRA-1470-v7-for-0.7.patch, CASSANDRA-1470-v8-for-0.7.patch, CASSANDRA-1470-v9-for-0.7.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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