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https://issues.apache.org/jira/browse/CASSANDRA-6357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13895739#comment-13895739
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Aleksey Yeschenko edited comment on CASSANDRA-6357 at 2/8/14 10:14 PM:
-----------------------------------------------------------------------
DD.applyConfig() logic should be altered:
{code}
else if (conf.memtable_flush_writers == null)
{
conf.memtable_flush_writers = conf.data_file_directories.length;
}
{code}
Directories.SSTableLister seems to not include the flush directory, which would
break Standalone{Upgrader, Splitter, Scrubber} and a bunch of other stuff using
the lister.
That, and I think we should support configuring multiple flush directories from
the very beginning, even if most users will use none or one.
was (Author: iamaleksey):
DD.applyConfig()
> Flush memtables to separate directory
> -------------------------------------
>
> Key: CASSANDRA-6357
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6357
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: Patrick McFadin
> Assignee: Jonathan Ellis
> Priority: Minor
> Fix For: 2.0.6
>
> Attachments: 6357-v2.txt, 6357.txt,
> c6357-stress-write-latency-99th-1.png
>
>
> Flush writers are a critical element for keeping a node healthy. When several
> compactions run on systems with low performing data directories, IO becomes a
> premium. Once the disk subsystem is saturated, write IO is blocked which will
> cause flush writer threads to backup. Since memtables are large blocks of
> memory in the JVM, too much blocking can cause excessive GC over time
> degrading performance. In the worst case causing an OOM.
> Since compaction is running on the data directories. My proposal is to create
> a separate directory for flushing memtables. Potentially we can use the same
> methodology of keeping the commit log separate and minimize disk contention
> against the critical function of the flushwriter.
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