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From "Marcus Eriksson (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-11623) Compactions w/ Short Rows Spending Time in getOnDiskFilePointer
Date Fri, 22 Apr 2016 13:26:12 GMT


Marcus Eriksson commented on CASSANDRA-11623:

Nice catch!

It looks like we could just use the [chunkOffset|]
directly instead though? Old getOnDiskFilePointer() should always be [exactly the same|]
as the chunkOffset

> 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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