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From "T Jake Luciani (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11623) Compactions w/ Short Rows Spending Time in getOnDiskFilePointer
Date Mon, 02 May 2016 21:09:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15267513#comment-15267513
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T Jake Luciani commented on CASSANDRA-11623:
--------------------------------------------

Related: CASSANDRA-11697

> 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
>            Assignee: Tom Petracca
>            Priority: Minor
>             Fix For: 3.x
>
>         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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