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From "Jonathan Ellis (Updated) (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-3411) Pre-allocated, Recycled Commitlog Segment Files
Date Fri, 28 Oct 2011 04:52:32 GMT


Jonathan Ellis updated CASSANDRA-3411:

    Attachment: 3411-cleaned.txt

attaching -cleaned, which is mostly undoing some renaming that obscured the real changes here.

I think there's some work to do around the commitlog preallocation:
- Seems like we should try to keep an extra segment ready, so that after we exhaust our preallocated
quota we don't block for each new segment
- segments to keep around should be our high water mark of active
- if we record that high water mark in the system table, that feels like a better way of self-tuning
to me than exposing the preallocation count as a tuneable
- segment allocation should be done off of the CLExecutor thread.  if we make "segments" just
"inactive segments" instead of "all segments" then we can make it into a blocking queue for
that purpose
> 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,
> 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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