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From "Pavel Yaskevich (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3950) support trickling fsync() on writes
Date Thu, 23 Feb 2012 20:56:49 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3950?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13215041#comment-13215041
] 

Pavel Yaskevich commented on CASSANDRA-3950:
--------------------------------------------

few last nits:

# inside of your if condition you still use bytesSinceCacheFlush instead of bytesSinceTrickleFsync
to set it to 0.
# "Requires JNA." can be removed from comment in conf/cassandra.yaml since build-in getFD().sync()
is used.
                
> support trickling fsync() on writes
> -----------------------------------
>
>                 Key: CASSANDRA-3950
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3950
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Peter Schuller
>            Assignee: Peter Schuller
>             Fix For: 1.1.0
>
>         Attachments: CASSANDRA-3950-1.1-v2.txt, CASSANDRA-3950-1.1.txt
>
>
> Attaching a patch to support fsync():ing every N megabytes of data written using sequential
writers. The motivation is to avoid the kernel flushing out pages in bulk.
> It makes sense for both platters and SSD:s, but it's particularly good for SSD:s because
the negative consequences of fsync():ing more often are much more limited than with platters,
and the *need* is to some extent greater because of the fact that with SSD:s you're much more
likely to be e.g. streaming data quickly or compacting quickly, since you're not having to
throttle everything as extremely as with platters, and you easily write fast enough for this
to be a problem if you're targetting good latency at the outliers.
> I'm nominating it for 1.1.0 because, if disabled, the probability of this being a regression
seems very low.

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