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From "Tom Petracca (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11623) Compactions w/ Short Rows Spending Time in getOnDiskFilePointer
Date Wed, 20 Apr 2016 18:44:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15250483#comment-15250483
] 

Tom Petracca commented on CASSANDRA-11623:
------------------------------------------

A solution to this is to just estimate the size of the written file.
https://github.com/tpetracca/cassandra/commit/d9028ce6be8956279807b428ff55d38ae759b1de

> Compactions w/ Short Rows Spending Time in getOnDiskFilePointer
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-11623
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11623
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Tom Petracca
>            Priority: Minor
>         Attachments: compactiontask_profile.png
>
>
> Been doing some performance tuning and profiling of my cassandra cluster and noticed
that compaction speeds for my tables that I know to have very short rows were going particularly
slowly.  Profiling shows a ton of time being spent in BigTableWriter.getOnDiskFilePointer(),
and attaching strace to a CompactionTask shows that a majority of time is being spent lseek
(called by getOnDiskFilePointer), and not read or write.
> Going deeper it looks like we call getOnDiskFilePointer each row (sometimes multiple
times per row) in order to see if we've reached our expected sstable size and should start
a new writer.  This is pretty unnecessary.



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