[jira] [Updated] (CASSANDRA-11623) Compactions w/ Short Rows Spending Time in getOnDiskFilePointer

["Marcus Eriksson (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-11623?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Marcus Eriksson updated CASSANDRA-11623:
----------------------------------------
       Resolution: Fixed
    Fix Version/s:     (was: 3.x)
                   3.8
           Status: Resolved  (was: Patch Available)

and committed, thanks for the patch!

> 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: 3.8
>
>         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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