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From "Rick Branson (Commented) (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-3411) Pre-allocated, Recycled Commitlog Segment Files
Date Thu, 10 Nov 2011 06:29:51 GMT


Rick Branson commented on CASSANDRA-3411:

Recycling the replayed segments is a good idea. Very elegant.

I wasn't quite sure how strict the cap limit was -- 004 tries to hit the cap with a "best
effort" and doesn't really treat it as a hard limit. If it's strict-in-bold it definitely
needs to be reworked. CommitLog should detect a potential overflow before it even allows the
write to take place and "stop the world" to perform a flush.

submitCreateFreshSegment was an oversight for sure, a refactor relic.

CLS.recycle() returning a new CLS is more of a preference than anything else -- I tend to
reach for more immutability when it doesn't hurt, and overall it seemed to be a cleaner approach
than reseting the state.

You have a good point about the order of shutdownBlocking, and actually, is the sync() even
necessary here or is it cargo cult? 
> 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,
3411-cleaned.txt, 3411-v5.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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