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From "Marcus Eriksson (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-12228) Write performance regression in 3.x vs 3.0
Date Tue, 02 Aug 2016 14:44:20 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15404078#comment-15404078
] 

Marcus Eriksson edited comment on CASSANDRA-12228 at 8/2/16 2:43 PM:
---------------------------------------------------------------------

Since 6696 the configuration sets how many flush writers there should be *per data directory*
- so factoring in the number of data directories in the calculation is probably wrong (ie,
with 10 data directories and 2 memtable flush writers you would get 20 threads actually doing
writing to disk and 2 threads waiting on the writing, meaning we can flush 2 memtables concurrently)

edit: re-read your yaml comment where you explain exactly what I wrote above :) - but why
would we want more threads per data directory if we have more data directories?


was (Author: krummas):
Since 6696 the configuration sets how many flush writers there should be *per data directory*
- so factoring in the number of data directories in the calculation is probably wrong (ie,
with 10 data directories and 2 memtable flush writers you would get 20 threads actually doing
writing to disk and 2 threads waiting on the writing, meaning we can flush 2 memtables concurrently)



> 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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