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https://issues.apache.org/jira/browse/CASSANDRA-1083?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ryan King updated CASSANDRA-1083:
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Attachment: compaction_simulation.rb
I wrote this ruby script to simulate what would happen with my proposal.
It does, indeed, keep the number of SSTables bounded, but at the cost of doing
more re-compactions of data. Once you hit the steady state the number of
compactions goes up (you're basically doing one every minCompationThreshold
flushes).
It seems to me like we need to find some compromise here.
> Improvement to CompactionManger's submitMinorIfNeeded
> -----------------------------------------------------
>
> Key: CASSANDRA-1083
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1083
> Project: Cassandra
> Issue Type: Improvement
> Affects Versions: 0.6.1
> Reporter: Ryan King
> Assignee: Ryan King
> Priority: Minor
> Attachments: 1083-configurable-compaction-thresholds.patch,
> compaction_simulation.rb
>
>
> We've discovered that we are unable to tune compaction the way we want for
> our production cluster. I think the current algorithm doesn't do this as well
> as it could, since it doesn't sort the sstables by size before doing the
> bucketing, which means the tuning parameters have unpredictable results.
> I looked at CASSANDRA-792, but it seems like overkill. Here's an alternative
> proposal:
> config operations:
> minimumCompactionThreshold
> maximumCompactionThreshold
> targetSSTableCount
> The first two would mean what they currently mean: the bounds on how many
> sstables to compact in one compaction operation. The 3rd is a target for how
> many SSTables you'd like to have.
> Pseudo code algorithm for determining whether or not to do a minor compaction:
> {noformat}
> if sstables.length + minimumCompactionThreshold -1 > targetSSTableCount
> sort sstables from smallest to largest
> compact the up to maximumCompactionThreshold smallest tables
> {noformat}
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