Details
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Improvement
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Status: Open
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Low
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Resolution: Unresolved
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None
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None
Description
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.