[jira] [Commented] (CASSANDRA-12300) Disallow unset memtable_cleanup_threshold when flush writers is set

["Ariel Weisberg (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-12300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15394194#comment-15394194 ] 

Ariel Weisberg commented on CASSANDRA-12300:
--------------------------------------------

I don't follow how you can do anything useful with MCT in general. If you increase flush writers you need a corresponding decrease in MCT to trigger more flushes to take advantage of the additional threads. Otherwise the additional threads will never be used because writes will block on available memory before more flushes can be started.

> Disallow unset memtable_cleanup_threshold when flush writers is set
> -------------------------------------------------------------------
>
>                 Key: CASSANDRA-12300
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12300
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Brandon Williams
>
> Many times I see flush writers set, and mct unset, leading to a very small mct, which causes unneeded frequent flushing, and then of course compaction.  I also think the default is a bit conservative, typically ending up at 0.11, where I'd say the majority of use cases only have one or two hot tables and are much better served at 0.7 or 0.8.



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