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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Assigned: (CASSANDRA-1083) Improvement to CompactionManger's submitMinorIfNeeded
Date Mon, 06 Dec 2010 20:43:10 GMT


Jonathan Ellis reassigned CASSANDRA-1083:

    Assignee: Tyler Hobbs  (was: Ryan King)

Tyler, do you see any low-hanging fruit here?  We also have CASSANDRA-1608 open for more invasive
changes, but if there is a free lunch lurking here let's grab that first.

> Improvement to CompactionManger's submitMinorIfNeeded
> -----------------------------------------------------
>                 Key: CASSANDRA-1083
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Ryan King
>            Assignee: Tyler Hobbs
>            Priority: Minor
>             Fix For: 0.7.1
>         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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