[jira] [Updated] (CASSANDRA-6357) Flush memtables to separate directory

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-6357?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jonathan Ellis updated CASSANDRA-6357:
--------------------------------------

    Attachment: 6357-v2.txt

v2 attached that handles blacklisted-flush-location

> Flush memtables to separate directory
> -------------------------------------
>
>                 Key: CASSANDRA-6357
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6357
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Patrick McFadin
>            Assignee: Jonathan Ellis
>             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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