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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-6357) Flush memtables to separate directory
Date Mon, 10 Feb 2014 20:05:20 GMT

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

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

    Fix Version/s:     (was: 2.0.6)
                   2.1

v3 pushed to https://github.com/jbellis/cassandra/commits/6357-3, with some renaming pulled
into a separate commit.

bit messier than I was hoping so retargetting for 2.1.

> 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: 2.1
>
>         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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