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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1470) use direct io for compaction
Date Wed, 08 Dec 2010 14:04:02 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12969317#action_12969317
] 

Pavel Yaskevich commented on CASSANDRA-1470:
--------------------------------------------

System: Quad-Core AMD Opteron(tm) Processor 2374 HE, 2 Gb RAM, Debian (2.6.35.4-rscloud SMP)

Test (using stress.py from T Jake comment):

          byte[] | Direct I/O (this shows elapsed_time)
-----------------------------
write |  113 | 511
-----------------------------
read |  225 | 213
-----------------------------
read |  175 | 205
-----------------------------
write |  118 | 567
-----------------------------
read |  219 | 207
-----------------------------

Write with Direct I/O should be slower comparing to write using kernel buffering + page writeback...



> 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-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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