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From "Marcus Eriksson (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-11623) Compactions w/ Short Rows Spending Time in getOnDiskFilePointer
Date Mon, 25 Apr 2016 07:28:13 GMT


Marcus Eriksson commented on CASSANDRA-11623:

I updated the patch and pushed it here:
- return chunkOffset
- rename the method to getEstimatedOnDiskBytesWritten
- reverted the test change as behavior should be exactly the same as before now

and tests are running here:

And unless there is a dramatic compaction performance difference I think we should only commit
this to trunk

[~philipthompson] or [~mshuler] could you test that branch for compaction performance?

> Compactions w/ Short Rows Spending Time in getOnDiskFilePointer
> ---------------------------------------------------------------
>                 Key: CASSANDRA-11623
>                 URL:
>             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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