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Ariel Weisberg commented on CASSANDRA-12228:
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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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