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From "Rick Branson (Updated) (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-3411) Pre-allocated, Recycled Commitlog Segment Files
Date Thu, 17 Nov 2011 07:48:51 GMT


Rick Branson updated CASSANDRA-3411:

    Attachment: 006-pre-allocated-recycled-commitlog-segment-files-CASSANDRA-3411.patch

006 recycles commit log segments after recovery. This holds the segment count steady across
restarts. I removed the initial segment allocation as it seemed unnecessary after this change.

At this point, there's a deadlock condition that arises if the cap is held hard. If the cap
is hit, in order to make some room in the commit log, a memtable flush must take place. The
memtable flush thread submits a task for execution on the commit log thread, which is already
blocked waiting for the memtable flush to finish.
> 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,
> 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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