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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6809) Compressed Commit Log
Date Tue, 19 Aug 2014 14:37:18 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14102247#comment-14102247
] 

Benedict commented on CASSANDRA-6809:
-------------------------------------

bq. is better than using a simple file-level compression

* Don't want to bound by a single CPU performing compression/sync
* Reduced file system fragmentation through obeying the size limits (less and less of a problem
as we move to SSDs, but for HDDs pretty important for CL performance)


> Compressed Commit Log
> ---------------------
>
>                 Key: CASSANDRA-6809
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6809
>             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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