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Posted to commits@cassandra.apache.org by "Jonathan Ellis (Commented) (JIRA)" <ji...@apache.org> on 2011/11/22 23:40:40 UTC

[jira] [Commented] (CASSANDRA-622) Improve commitlog performance

    [ https://issues.apache.org/jira/browse/CASSANDRA-622?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13155520#comment-13155520 ] 

Jonathan Ellis commented on CASSANDRA-622:
------------------------------------------

CASSANDRA-3411 did the segment recycling described here.
                
> Improve commitlog performance
> -----------------------------
>
>                 Key: CASSANDRA-622
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-622
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Priority: Minor
>              Labels: gsoc, gsoc2010
>
> Postgresql uses fixed-size commitlog files that it pre-allocates (filling with zeros) so "appending" to the log can use cheaper fsync-without-metadata (length changes is "metadata").  Then, when a commitlog is not needed, it "recycles" it by renaming it to a higher number.  Commitlog entries have an increasing id, and if you come to an out-of-sequence (earlier) id, then you must have have reached the end of the commitlog and are reading from the "recycled" part.

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