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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-2427) Heuristic or hard cap to prevent fragmented commit logs from bringing down the server
Date Mon, 13 Jun 2011 22:35:48 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2427?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13048838#comment-13048838
] 

Jonathan Ellis commented on CASSANDRA-2427:
-------------------------------------------

That's a good stab at it.  I'd like to make a couple changes:

- the executor mbean should really be only for the executor.  Let's create a CommitLogMBean
where we expose this and the executor stats.  (IExecutorMBean can go away.)
- if we only check for flush-needed when we rotate the commitlog, "denormalizing" segment
total size is unnecessary -- let's just go through the segments collection and add up length()
on demand. Sorry for suggesting otherwise to start with!

> Heuristic or hard cap to prevent fragmented commit logs from bringing down the server
> -------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-2427
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2427
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benjamin Coverston
>            Assignee: Patricio Echague
>              Labels: commitlog, hardening
>             Fix For: 1.0
>
>         Attachments: CASSANDRA-2427-2-trunk-addNewSetting.txt, CASSANDRA-2427-Jconsole-snapshot.tiff,
CASSANDRA-2427-trunk.txt
>
>
> Widely divergent write rates on column families can cause the commit log segments to
fragment. In some cases we have seen the commit log partition overrun.
> One solution here would be to create a heuristic for segment fragmentation to trigger
a flush (commit log segments/memtable) or simply track the free disk space and force a global
flush when the disk gets to 80% capacity.

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