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From "Peter Schuller (Updated) (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-3950) support trickling fsync() on writes
Date Wed, 29 Feb 2012 06:27:58 GMT


Peter Schuller updated CASSANDRA-3950:

    Attachment: CASSANDRA-3950-1.1-v3.txt

{{v3}} attached. Third time's the charm. I made it {{in_kb}} instead too, because I realized
that megabyte resolution is not necessarily enough for really low-latency cases on a modern
SSD (1 MB for a 90 MB/sec seq. writing SSD is 11 milliseconds).
> support trickling fsync() on writes
> -----------------------------------
>                 Key: CASSANDRA-3950
>                 URL:
>             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-v3.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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