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https://issues.apache.org/jira/browse/CASSANDRA-3178?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sylvain Lebresne updated CASSANDRA-3178:
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Attachment: 0002-Simplify-improve-shard-merging-code-1.0.patch
0001-Move-shard-merging-completely-to-compaction-1.0.patch
Attaching patches rebased against 1.0
> Counter shard merging is not thread safe
> ----------------------------------------
>
> Key: CASSANDRA-3178
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3178
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 0.8.5
> Reporter: Sylvain Lebresne
> Assignee: Sylvain Lebresne
> Labels: counters
> Fix For: 0.8.8
>
> Attachments:
> 0001-Move-shard-merging-completely-to-compaction-1.0.patch,
> 0001-Move-shard-merging-completely-to-compaction-v2.patch,
> 0001-Move-shard-merging-completely-to-compaction.patch,
> 0002-Simplify-improve-shard-merging-code-1.0.patch,
> 0002-Simplify-improve-shard-merging-code-v2.patch,
> 0002-Simplify-improve-shard-merging-code.patch
>
>
> The first part of the counter shard merging process is done during counter
> replication. This was done there because it requires that all replica are
> made aware of the merging (we could only rely on nodetool repair for that but
> that seems much too fragile, it's better as just a safety net). However this
> part isn't thread safe as multiple threads can do the merging for the same
> shard at the same time (which shouldn't really "corrupt" the counter value
> per se, but result in an incorrect context).
> Synchronizing that part of the code would be very costly in term of
> performance, so instance I propose to move the part of the shard merging done
> during replication to compaction. It's a better place anyway. The only
> downside is that it means compaction will sometime send mutations to other
> node as a side effect, which doesn't feel very clean but is probably not a
> big deal either.
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