Stefan Podkowinski created CASSANDRA-8979:
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Summary: MerkleTree mismatch for deleted and non-existing rows
Key: CASSANDRA-8979
URL: https://issues.apache.org/jira/browse/CASSANDRA-8979
Project: Cassandra
Issue Type: Bug
Components: Core
Reporter: Stefan Podkowinski
Validation compaction will currently create different hashes for rows that have
been deleted compared to nodes that have not seen the rows at all or have
already compacted them away.
In case this sounds familiar to you, see CASSANDRA-4905 which was supposed to
prevent hashing of expired tombstones. This still seems to be in place, but
does not address the issue completely. Or there was a change in 2.0 that
rendered the patch ineffective.
The problem is that rowHash() in the Validator will return a new hash in any
case, whether the PrecompactedRow did actually update the digest or not. This
will lead to the case that a purged, PrecompactedRow will not change the
digest, but we end up with a different tree compared to not having rowHash
called at all (such as in case the row already doesn't exist).
As an implication, repair jobs will constantly detect mismatches between older
sstables containing purgable rows and nodes that have already compacted these
rows. After transfering the reported ranges, the newly created sstables will
immediately get deleted again during the following compaction. This will happen
for each repair run over again until the sstable with the purgable row finally
gets compacted.
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