[CASSANDRA-4932] Agree on a gcbefore/expirebefore value for all replica during validation compaction

• Type: Improvement
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 2.0 beta 1
• Assignee: Marcus Eriksson
• Reporter: Sylvain Lebresne

Authors

Marcus Eriksson

Reviewers

Yuki Morishita

• Created: 08/Nov/12 10:13
• Updated: 16/Apr/19 09:32
• Resolved: 09/Apr/13 06:13

Description

CASSANDRA-4905 made it so that we don't include gcable tombstones in merkle tree digests because otherwise the fact that a gcable tombstone exists in a given node depends on the local scheduling of compactions, which make the merkle-tree digets depends on that which is bad.

However, we still depends on a value of gcbefore/expirebefore that is computed locally on the node. This is not a huge deal because each node should compute those value roughly at the same time so the discrepancies shouldn't exceed a few hundreds of milliseconds in general and a few seconds if we're unlucky. Still, it's fairly easy to fix this problem by having the repair coordinator pick the gcbefore/expirebefore and share that with all the replica. It does require sending that info on the wire though, so will require a new messaging version and thus can only be done in a major cycle.

Issue Links

• relates to: CASSANDRA-4905 Repair should exclude gcable tombstones from merkle-tree computation