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Date: Tue, 22 Nov 2011 18:32:39 +0000 (UTC)
From: "Rick Branson (Commented) (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-3411) Pre-allocated, Recycled
 Commitlog Segment Files
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    [ https://issues.apache.org/jira/browse/CASSANDRA-3411?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13155329#comment-13155329 ] 

Rick Branson commented on CASSANDRA-3411:
-----------------------------------------

Nice, definitely some refactoring that needed to be done I was a little conservative about, specifically moving more work into the CommitLogAllocator and that magic flag ;) We discussed elsewhere that this patch will enforce a commit segment size (128MB) limit on the row mutation size, which needs to be communicated to the users via the NEWS or CHANGES files. I also didn't see anything that would catch a mutation that was too large and log an error. This could lead to some pretty nasty behavior if the user attempts to do such a thing.
                
> Pre-allocated, Recycled Commitlog Segment Files
> -----------------------------------------------
>
>                 Key: CASSANDRA-3411
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3411
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Rick Branson
>            Priority: Minor
>         Attachments: 001-pre-allocated-recycled-commitlog-segment-files-CASSANDRA-3411.patch, 003-pre-allocated-recycled-commitlog-segment-files-CASSANDRA-3411.patch, 004-pre-allocated-recycled-commitlog-segment-files-CASSANDRA-3411.patch, 006-pre-allocated-recycled-commitlog-segment-files-CASSANDRA-3411.patch, 3411-cleaned.txt, 3411-v5.txt, 3411-v6-retry.txt, 3411-v7.txt
>
>
> An approach for improving commitlog performance is to pre-allocate the full 128MB segment files and reuse them once all the mutations have been flushed. Pre-allocation allows writes to be performed without modifying the file size metadata, and should (in theory) allow the filesystem to allocate a contiguous block of space for the file. Recycling the segment files prevents the overhead of pre-allocation from impacting overall performance.

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