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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12228) Write performance regression in 3.x vs 3.0
Date Tue, 02 Aug 2016 17:28:20 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15404434#comment-15404434
] 

Ariel Weisberg commented on CASSANDRA-12228:
--------------------------------------------

I think the default can be really simple. If there are multiple data directories use a value
of 1 so concurrency will be # of data directories and there will be a single memtable flush.
If there is a single directory set it to 2 so there can be two concurrent memtable flushes
to the single data directory.

If the user specifies a # of concurrent memtable flushes we honor that by providing enough
threads to wait on the flushes as well as enough threads per disk that each memtable can flush
concurrently.

I pushed an updated version reflecting this change. There is also a commit that removes memtable_cleanup_threshold.



> Write performance regression in 3.x vs 3.0
> ------------------------------------------
>
>                 Key: CASSANDRA-12228
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12228
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: T Jake Luciani
>            Assignee: Ariel Weisberg
>            Priority: Minor
>             Fix For: 3.9
>
>
> I've been tracking down a performance issue in trunk vs cassandra-3.0 branch.
> I think I've found it.  CASSANDRA-6696 changed the default memtable flush default to
1 vs the min of 2 in cassandra-3.0.
> I don't see any technical reason for this and we should add back the min of 2 sstable
flushers per disk.



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