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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-6357) Flush memtables to separate directory
Date Wed, 23 Apr 2014 20:20:16 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13978837#comment-13978837
] 

Benedict edited comment on CASSANDRA-6357 at 4/23/14 8:18 PM:
--------------------------------------------------------------

+1 general sentiment, but not sure the revert patch is correct: at the very least the anti-compaction
part changing sstableAsSet breaks 6916

That might be my fault for not commenting the fact that SSTableRewriter expects a mutable
set though.


was (Author: benedict):
+1 general sentiment, but not sure the revert patch is correct: at the very least the anti-compaction
part changing sstableAsSet breaks 6916

> 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
>              Labels: performance
>             Fix For: 2.1 beta1
>
>         Attachments: 6357-revert.txt, 6357-v2.txt, 6357.txt, c6357-2.1-stress-write-adj-ops-sec.png,
c6357-2.1-stress-write-latency-99th.png, c6357-2.1-stress-write-latency-median.png, 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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