[HBASE-23282] HBCKServerCrashProcedure for 'Unknown Servers'

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.2.2
• Fix Version/s: 3.0.0-alpha-1, 2.3.0, 2.2.3
• Component/s: hbck2, proc-v2
• Release Note: hbck2 scheduleRecoveries will now run a SCP that also looks in hbase:meta for any references to the scheduled server -- not just consult Master in-memory state -- just in case vestiges of the server are leftover in hbase:meta
• Assignee: Michael Stack
• Reporter: Michael Stack
• Created: 13/Nov/19 00:50
• Updated: 15/Feb/20 22:02
• Resolved: 18/Nov/19 22:37

Description

With an overdriving, sustained load, I can fairly easily manufacture an hbase:meta table that references servers that are no longer in the live list nor are members of deadservers; i.e. 'Unknown Servers'. The new 'HBCK Report' UI in Master has a section where it lists 'Unknown Servers' if any in hbase:meta.

Once in this state, the repair is awkward. Our assign/unassign Procedure is particularly dogged about insisting that we confirm close/open of Regions when it is going about its business which is well and good if server is in live/dead sets but when an 'Unknown Server', we invariably end up trying to confirm against a non-longer present server (More on this in follow-on issues).

What is wanted is queuing of a ServerCrashProcedure for each 'Unknown Server'. It would split any WALs (there shouldn't be any if server was restarted) and ideally it would cancel out any assigns and reassign regions off the 'Unknown Server'. But the 'normal' SCP consults the in-memory cluster state figuring what Regions were on the crashed server... And 'Unknown Servers' don't have state in in-master memory Maps of Servers to Regions or in DeadServers list which works fine for the usual case.

Suggestion here is that hbck2 be able to drive in a special SCP, one which would get list of Regions by scanning hbase:meta rather than asking Master memory; an HBCKSCP.

Issue Links

• breaks: HBASE-23596 HBCKServerCrashProcedure can double assign
• is related to: HBASE-23247 [hbck2] Schedule SCPs for 'Unknown Servers'
• links to: GitHub Pull Request #826

Sub-Tasks

• [hbck2] Simplification on HBCKSCP scheduling: Resolved