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https://issues.apache.org/jira/browse/CASSANDRA-6357?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis updated CASSANDRA-6357:
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Attachment: 6357.txt
Patch that allows splitting out {{flush_directory}} to a separate volume,
defaulting to /var/lib/cassandra/flush once patched.
Note that it will default to the first data directory if you upgrade without
specifying {{flush_directory}}, so you do need to remember to set it because it
won't bitch at you if you don't.
> Flush memtables to seperate directory
> -------------------------------------
>
> Key: CASSANDRA-6357
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6357
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Patrick McFadin
> Attachments: 6357.txt
>
>
> 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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