stack created HBASE-18551:

             Summary: [AMv2] UnassignProcedure and crashed regionservers
                 Key: HBASE-18551
             Project: HBase
          Issue Type: Bug
          Components: amv2
            Reporter: stack

This has been [~uagashe] and my obsession over the last few days, what should 
an UnassignProcedure do when it dispatches a CLOSE but the CLOSE fails because 
of ConnectException or SocketTimeout.

+ We used to let UnassignProcedure continue presuming the Region would be 
closed since the server is dead. BUT, if the unassign was part of a 
MoveProcedure, the unassign would proceed and the Move would then run WITHOUT 
first splitting logs. Bad.
+ So, we made it so UnassignProcedure failed; let the upper layers take care of 
the failure. See HBASE-18491 that enabled this behavior. BUT, we are since 
figuring that even if the UP completes as a failure, since it gives up the 
Region lock on completion, another procedure -- say an AssignProcedure -- could 
cut in before the ServerCrashProcedure had finished and again there could be 
+ Now we are thinking the UP should hold on to the Region lock until we are 
signalled by a ServerCrashProcedure; only then let go of the region. The UP has 
context that is hard to pass another. Waiting on a SCP has the UP living on for 
what could be a good amount of time. It might be ok if we can suspend the 

There is a good sample scenario that came up doing the no-regions-on-master 
issue, HBASE-18511. When meta is not on master, TestSplitTransactionOnCluster 
is failing. It fails because though the test completes, the tests commonly kill 
a RegionServer. The teardown for the test runs before we've noticed the aborted 
RS. So, the disable of the table in the teardown prepartory to our deleting the 
test table as part of clean up, goes to unassign regions but the unassign fails 
against the aborted server.

Good stuff.

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