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From "Rick Branson (Issue Comment Edited) (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Edited] (CASSANDRA-3411) Pre-allocated, Recycled Commitlog Segment Files
Date Thu, 27 Oct 2011 17:52:32 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3411?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13137324#comment-13137324
] 

Rick Branson edited comment on CASSANDRA-3411 at 10/27/11 5:51 PM:
-------------------------------------------------------------------

This patch pre-allocates the 128MB segment files, writes using memory-mapped I/O, and recycles
the segment files once they're safe to be reused. End-to-end performance gains found across
the board, increasing with the size of the row mutation.

EDIT: should also mention that the number of segments initially allocated is controlled by
commitlog_preallocate_segments in cassandra.yaml and defaults to 4. If more are needed, they
will be created on-demand and deleted when no longer necessary.
                
      was (Author: rbranson):
    This patch pre-allocates the 128MB segment files, writes using memory-mapped I/O, and
recycles the segment files once they're safe to be reused. End-to-end performance gains found
across the board, increasing with the size of the row mutation.

EDIT: should also mention that the number of segments initially allocated is controlled by
commitlog_preallocate_segments in cassandra.yaml and defaults to 4. If more than 4 commit
log segments are needed, they will be created on-demand and deleted when no longer necessary.
                  
> 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
>
>
> 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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