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From "Branimir Lambov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6809) Compressed Commit Log
Date Tue, 03 Feb 2015 17:46:36 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14303660#comment-14303660
] 

Branimir Lambov commented on CASSANDRA-6809:
--------------------------------------------

Yes, this is the expected behaviour. The rationale is in the discussion above-- compression
with a fixed size of the compressed segment is quite a bit more complex as it requires a level
of "microsegments" that mutation threads write in, in addition to what exists now.

> 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
>
>         Attachments: ComitLogStress.java, logtest.txt
>
>
> 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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