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https://issues.apache.org/jira/browse/CASSANDRA-6809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14303633#comment-14303633
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Alan Boudreault commented on CASSANDRA-6809:
--------------------------------------------

[~barnie] Can you confirm if this is the desired behavior? Using 
commitlog_compression, the commitlog files created on disk are smaller than 
what we set in cassandra.yaml. Using default configuration, commitlogs are 23MB 
rather than 32MB. I thought that the compression would only affect the data 
written inside the commitlogs, and not the file size itself. 

> 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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