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https://issues.apache.org/jira/browse/CASSANDRA-3411?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13137324#comment-13137324
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Rick Branson edited comment on CASSANDRA-3411 at 10/27/11 5:51 PM:
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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.
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.
> 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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