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Date: Tue, 3 Feb 2015 17:46:36 +0000 (UTC)
From: "Branimir Lambov (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12699251.1394135641000.243747.1422985596580@Atlassian.JIRA>
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 <JIRA.12699251.1394135641575@arcas>
Subject: [jira] [Commented] (CASSANDRA-6809) Compressed Commit Log
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    [ 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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