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https://issues.apache.org/jira/browse/CASSANDRA-4071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13482376#comment-13482376
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Sylvain Lebresne commented on CASSANDRA-4071:
---------------------------------------------
I'm starting to wonder if we shouldn't just create a separate streaming for
counter that would merge everything it has to stream on the fly and stream that
(not likely our old anti-compaction). That would pretty much be equivalent to
my solution above of "doing a major compaction on the source before doing any
streaming", but it would suck a little bit less (not by much but I don't have a
better solution so far). Of course that would make streaming much less
efficient for counters column families (on top of the pain of having two
completely different path for streaming).
> Topology changes can lead to bad counters (at RF=1)
> ---------------------------------------------------
>
> Key: CASSANDRA-4071
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4071
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.0.0
> Reporter: Sylvain Lebresne
> Labels: counters
>
> A counter is broken into shards (partitions), each shard being 'owned' by a
> given replica (meaning that only this replica will increment that shard).
> For a given node A, the resolution of 2 shards (having the same owner)
> follows the following rules:
> * if the shards are owned by A, then sum the values (in the original patch,
> 'owned by A' was based on the machine IP address, in the current code, it's
> based on the shard having a delta flag but the principle is the same)
> * otherwise, keep the maximum value (based on the shards clocks)
> During topology changes (boostrap/move/decommission), we transfer data from A
> to B, but the shards owned by A are not owned by B (and we cannot make them
> owned by B because during those operations (boostrap, ...) a given shard
> would be owned by A and B which would break counters). But this means that B
> won't interpret the streamed shards correctly.
> Concretely, if A receives a number of counter increments that end up in
> different sstables (the shards should thus be summed) and then those
> increments are streamed to B as part of boostrap, B will not sum the
> increments but use the clocks to keep the maximum value.
> I've pushed a test that show the breakeage at
> https://github.com/riptano/cassandra-dtest/commits/counters_test (the test
> needs CASSANDRA-4070 to work correctly).
> Note that in practice, replication will hide this (even though B will have
> the bad value after the boostrap, read or read/repair from the other replica
> will repair it). This is a problem for RF=1 however.
> Another problem is that during repair, a node won't correctly repair other
> nodes on it's own shards (unless everything is fully compacted).
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