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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6809) Compressed Commit Log
Date Fri, 05 Sep 2014 10:03:28 GMT


Benedict commented on CASSANDRA-6809:

I'm +1 on your over all intended approach, but I'd appreciate some elaboration on what steps
you've taken for testing:

* What platforms?
* What CPU config?
* What measurement of CPU time allocation? (10-20% bump may be reasonable if its kernel time,
but I'm a little surprised it has such an impact, as we'd be talking about bulk writing large
quantities of linear data, which should have reasonably low CPU impact)

If you could post your in progress branches and tests to github so I can follow what you're
doing, that would be great

> Compressed Commit Log
> ---------------------
>                 Key: CASSANDRA-6809
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benedict
>            Assignee: Branimir Lambov
>            Priority: Minor
>              Labels: performance
>             Fix For: 3.0
> It seems an unnecessary oversight that we don't compress the commit log. Doing so should
improve throughput, but some care will need to be taken to ensure we use as much of a segment
as possible. I propose decoupling the writing of the records from the segments. Basically
write into a (queue of) DirectByteBuffer, and have the sync thread compress, say, ~64K chunks
every X MB written to the CL (where X is ordinarily CLS size), and then pack as many of the
compressed chunks into a CLS as possible.

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