[HBASE-14802] Replaying server crash recovery procedure after a failover causes incorrect handling of deadservers

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.2.0, 1.2.1, 2.0.0
• Fix Version/s: 1.2.0, 1.3.0, 2.0.0
• Component/s: master
• Hadoop Flags: Reviewed
• Assignee: Ashu Pachauri
• Reporter: Ashu Pachauri
• Created: 12/Nov/15 22:09
• Updated: 16/Nov/15 03:42
• Resolved: 15/Nov/15 23:02

Description

The way dead servers are processed is that a ServerCrashProcedure is launched for a server after it is added to the dead servers list.
Every time a server is added to the dead list, a counter "numProcessing" is incremented and it is decremented when a crash recovery procedure finishes. Since, adding a dead server and recovering it are two separate events, it can cause inconsistencies.

If a master failover occurs in the middle of the crash recovery, the numProcessing counter resets but the ServerCrashProcedure is replayed by the new master. This causes the counter to go negative and makes the master think that dead servers are still in process of recovery.
This has ramifications on the balancer that the balancer ceases to run after such a failover.