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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11035) Use cardinality estimation to pick better compaction candidates for STCS (SizeTieredCompactionStrategy)
Date Thu, 04 Feb 2016 01:29:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11035?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15131512#comment-15131512
] 

Jonathan Ellis commented on CASSANDRA-11035:
--------------------------------------------

The problem here was, you end up doing quadratic work comparing each sstable to each other
to find the best candidates to merge.  So the question is, do we try to come up with a clever
way to avoid this?  Or do we go ahead and brute force it, which would require updating HyperLogLog
to use off-heap registers?  (The latter actually looks pretty easy, now that I check the source.)

> Use cardinality estimation to pick better compaction candidates for STCS (SizeTieredCompactionStrategy)
> -------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-11035
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11035
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Compaction
>            Reporter: Wei Deng
>
> This was initially mentioned in this blog post http://www.datastax.com/dev/blog/improving-compaction-in-cassandra-with-cardinality-estimation
but I couldn't find any existing JIRA for it. As stated by [~jbellis], "Potentially even more
useful would be using cardinality estimation to pick better compaction candidates. Instead
of blindly merging sstables of a similar size a la SizeTieredCompactionStrategy." The L0 STCS
in LCS should benefit as well.



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