C. Scott Andreas updated CASSANDRA-12991:
    Component/s: Repair

> Inter-node race condition in validation compaction
> --------------------------------------------------
>                 Key: CASSANDRA-12991
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12991
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Repair
>            Reporter: Benjamin Roth
>            Priority: Minor
> Problem:
> When a validation compaction is triggered by a repair it may happen that due 
> to flying in mutations the merkle trees differ but the data is consistent 
> however.
> Example:
> t = 10000: 
> Repair starts, triggers validations
> Node A starts validation
> t = 10001:
> Mutation arrives at Node A
> t = 10002:
> Mutation arrives at Node B
> t = 10003:
> Node B starts validation
> Hashes of node A+B will differ but data is consistent from a view (think of 
> it like a snapshot) t = 10000.
> Impact:
> Unnecessary streaming happens. This may not a big impact on low traffic CFs, 
> partitions but on high traffic CFs and maybe very big partitions, this may 
> have a bigger impact and is a waste of resources.
> Possible solution:
> Build hashes based upon a snapshot timestamp.
> This requires SSTables created after that timestamp to be filtered when doing 
> a validation compaction:
> - Cells with timestamp > snapshot time have to be removed
> - Tombstone range markers have to be handled
>  - Bounds have to be removed if delete timestamp > snapshot time
>  - Boundary markers have to be either changed to a bound or completely 
> removed, depending if start and/or end are both affected or not
> Probably this is a known behaviour. Have there been any discussions about 
> this in the past? Did not find an matching issue, so I created this one.
> I am happy about any feedback, whatsoever.

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