[ZOOKEEPER-1291] AcceptedEpoch not updated at leader before it proposes the epoch to followers

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.0
• Fix Version/s: 3.4.0, 3.5.0
• Component/s: server
• Release Note: Revision 1198053
• Assignee: Alexander Shraer
• Reporter: Alexander Shraer
• Created: 05/Nov/11 20:01
• Updated: 21/Dec/23 11:33
• Resolved: 05/Nov/11 20:59

Description

It is possible that a leader proposes an epoch e and a follower adopts it by setting acceptedEpoch to e but the leader itself hasn't yet done so.

While I'm not sure this contradicts Zab (there is no description of where the leader actually sets its acceptedEpoch), it is very counter intuitive.

The fix is to set acceptedEpoch in getEpochToPropose, i.e., before anyone LearnerHandler passes the getEpochToPropose barrier.

The fix is done as part of ZK-1264

Issue Links

• relates to: ZOOKEEPER-4781 ZooKeeper not starting because the accepted epoch is less than the current epoch.