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https://issues.apache.org/jira/browse/CASSANDRA-1876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12973420#action_12973420
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Germán Kondolf commented on CASSANDRA-1876:
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In the minor logical compaction process we reduce the column versions and write 
only the latest version to the new index and filter, this will cause orphan 
blocks inside the immutable SSTables, that will be cleared in a major 
compaction.

> Allow minor Parallel Compaction
> -------------------------------
>
>                 Key: CASSANDRA-1876
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1876
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Germán Kondolf
>            Priority: Minor
>         Attachments: 1876-reformatted.txt, compactionPatch-V2.txt
>
>
> Hi,
> According to the dev's list discussion (1) I've patched the CompactionManager 
> to allow parallel compaction.
> Mainly it splits the sstables to compact in the desired buckets, configured 
> by a new parameter: compaction_parallelism with the current default of "1".
> Then, it just submits the units of work to a new executor and waits for the 
> finalization.
> The patch was created in the trunk, so I don't know the exact affected 
> version, I assume that is 0.8.
> I'll try to apply this patch to 0.6.X also for my current production 
> installation, and then reattach it.
> (1) http://markmail.org/thread/cldnqfh3s3nufnke

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