[CASSANDRA-15462] Purgable tombstones can cause false positives in repaired data tracking

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 4.0-alpha3, 4.0
• Component/s: Observability/Metrics
• Bug Category: Correctness
• Severity: Normal
• Complexity: Normal
• Discovered By: Code Inspection
• Platform: All
• Since Version: 4.0-alpha

Source Control Link

https://github.com/apache/cassandra/commit/9a280516ca8b9e730ae0648e5e29ee6280605132

Test and Documentation Plan

Updated unit and in-jvm dtests

• Assignee: Sam Tunnicliffe
• Reporter: Sam Tunnicliffe

Authors

Sam Tunnicliffe

Reviewers

Marcus Eriksson

• Created: 19/Dec/19 13:09
• Updated: 21/Dec/20 08:08
• Resolved: 23/Jan/20 10:20

Description

Calculating the repaired data digest on the read path (for the purposes of detecting mismatches in the repaired data across replicas) is done before purging any tombstones due to gcgs or last repaired time. This causes false positives when repaired sstables include GC-able tombstones on some replicas but not others.

Validation compactions do purge tombstones so it's perfectly possible for sstables to mismatch in this way without causing any streaming during repair.

Issue Links

• depends upon: CASSANDRA-15461 Legacy counter shards can cause false positives in repaired data tracking