[HBASE-28114] Add more comments to explain why replication log queue could never be empty for normal replication queue

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.6.0, 3.0.0-beta-1
• Component/s: Replication
• Hadoop Flags: Reviewed
• Assignee: Duo Zhang
• Reporter: Duo Zhang
• Created: 27/Sep/23 08:14
• Updated: 21/Oct/23 20:05
• Resolved: 20/Oct/23 14:37

Description

In HBASE-28037, Xiaolin Ha found that there could be a very small window that even for a normal replication source, its queue could be empty.

This is because we will only enqueue the wal file to the queue in postLogRoll, where the old WAL writer has already been closed, so if the replication is fast enough, we could reach the end of the queue before enqueuing the new wal file.

The code for branch-2+ has been refactored a lot so we opened a new issue for fixing this.

Issue Links

• is related to: HBASE-28037 Replication stuck after switching to new WAL but the queue is empty
• relates to: HBASE-28115 Deal with the replication queue empty problem for sync replication
• links to: GitHub Pull Request #5443