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https://issues.apache.org/jira/browse/CASSANDRA-12300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15394770#comment-15394770
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Brandon Williams commented on CASSANDRA-12300:
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I think part of it is our somewhat bad advice:
{noformat}
# If your data directories are backed by SSD, you should increase this
# to the number of cores.
#memtable_flush_writers: 8
{noformat}
Oh, I have SSD, I'll set this to the number of cores. In reality, I think what
you want to set this to is min(active_tables+fudge, num_cores). Instead when
you do just blindly set this to the number of cores, you can get a huge divisor
for mct if unset, and create a bunch of very small sstables (I've seen as bad
as a handful or two of kilobytes.)
> 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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