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From "Jonathan Ellis (Updated) (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-3411) Pre-allocated, Recycled Commitlog Segment Files
Date Tue, 22 Nov 2011 17:52:40 GMT


Jonathan Ellis updated CASSANDRA-3411:

    Attachment: 3411-v7.txt

v7 attached.

Cleaned out uses of CLS.length which were mostly incorrect now.

Cleaned up the size tracking code.

Made allocator responsible for recycle/discard decision.

Added enableReserveSegmentCreation "magic flag" to avoid so much churn on restart/reply.

Switched to pre-append capacity check instead of post-, so no need to mmap more than a single
buffer per segment.

Moved all segment tracking into allocator.

Will create tickets for switching to a txid-based reply, and saving the extra local copy.
> Pre-allocated, Recycled Commitlog Segment Files
> -----------------------------------------------
>                 Key: CASSANDRA-3411
>                 URL:
>             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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