Benjamin Roth created CASSANDRA-12991:
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Summary: Inter-node race condition in validation compaction
Key: CASSANDRA-12991
URL: https://issues.apache.org/jira/browse/CASSANDRA-12991
Project: Cassandra
Issue Type: Improvement
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 not consistent.
Example:
t = 10000:
Repair starts validation
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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