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From "Alex Tang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4316) Compaction Throttle too bursty with large rows
Date Fri, 21 Dec 2012 00:17:16 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537538#comment-13537538
] 

Alex Tang commented on CASSANDRA-4316:
--------------------------------------

<facepalm>.  Sorry about that. I misread it. Thanks.  

BTW, do you have an idea on what the method of fix is?  Is it going to be the OP's suggestion
to change how often the compaction happens or to perform a more complex calculation to make
sleeps more consistent?
                
> Compaction Throttle too bursty with large rows
> ----------------------------------------------
>
>                 Key: CASSANDRA-4316
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4316
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.8.0
>            Reporter: Wayne Lewis
>            Assignee: Yuki Morishita
>             Fix For: 1.2.1
>
>
> In org.apache.cassandra.db.compaction.CompactionIterable the check for compaction throttling
occurs once every 1000 rows. In our workload this is much too large as we have many large
rows (16 - 100 MB).
> With a 100 MB row, about 100 GB is read (and possibly written) before the compaction
throttle sleeps. This causes bursts of essentially unthrottled compaction IO followed by a
long sleep which yields inconsistence performance and high error rates during the bursts.
> We applied a workaround to check throttle every row which solved our performance and
error issues:
> line 116 in org.apache.cassandra.db.compaction.CompactionIterable:
>                 if ((row++ % 1000) == 0)
> replaced with
>                 if ((row++ % 1) == 0)
> I think the better solution is to calculate how often throttle should be checked based
on the throttle rate to apply sleeps more consistently. E.g. if 16MB/sec is the limit then
check for sleep after every 16MB is read so sleeps are spaced out about every second.

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