[HBASE-8545] Meta stuck in transition when it is assigned to a just restarted dead region sever

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.98.0, 0.95.1
• Component/s: Region Assignment
• Hadoop Flags: Reviewed
• Assignee: Jimmy Xiang
• Reporter: Jimmy Xiang
• Created: 14/May/13 17:04
• Updated: 19/Dec/13 22:33
• Resolved: 21/May/13 17:20

Description

Support the meta region server is down, and the SSH tries to re-assign it. This could happen:

1. AM plans to assign meta to a region server (R_old);
2. Now R_old is dead, the new region server (R_new) starts up on the same host, port, but gets a different start code;
3. AM sends the open region request to R_new and the Meta is opened on it;
4. AM gets ZK event, but it is from a different region server instance (R_new), not the expected one (R_old), so it sends a close region request to R_new;
5. Now, the meta is stuck in transition and won't be assigned.

This won't happen to a user region since the SSH for R_old will find out the user region stuck in transition and re-assign it. For meta, it is a little different. AM checks if a dead region server carries the meta based on the ZK info, which is changed to the new region server R_new at step 3 by the open region handler.

The fix I was thinking about is:
1. In checking if a region server carries a region, uses the region transition information if it exists (which is the source of truth, to master), if not, checks the ZK data as before;
2. In open region handler, when transition assign zk node from offline to opening, make sure the current region server is the expected one (ZK#transitionNode, existing code doesn't check the target server name).

Issue Links

• is related to: HBASE-9721 RegionServer should not accept regionOpen RPC intended for another(previous) server