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From "Stephen Yuan Jiang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17023) Region left unassigned due to AM and SSH each thinking others would do the assignment work
Date Fri, 04 Nov 2016 16:08:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15636838#comment-15636838

Stephen Yuan Jiang commented on HBASE-17023:

V0 patch proposed the fix in ClosedRegionHandler that we make sure that both last assigned
RS and current RS are the same.  This does not break existing tests that exercise the ClosedRegionHandler
code path.  

However, I tried very hard to mock the scenario; but I could not come up with a UT that simulate
this particular case (either the test does not exercise ClosedRegionHandler code path; or
exercise the ClosedRegionHandler code path, but not need the fix).  I am still working on
the UT.

> Region left unassigned due to AM and SSH each thinking others would do the assignment
> ------------------------------------------------------------------------------------------
>                 Key: HBASE-17023
>                 URL: https://issues.apache.org/jira/browse/HBASE-17023
>             Project: HBase
>          Issue Type: Bug
>          Components: Region Assignment
>    Affects Versions: 1.1.0
>            Reporter: Stephen Yuan Jiang
>            Assignee: Stephen Yuan Jiang
>         Attachments: HBASE-17023.v0-branch-1.1.patch
> Another Assignment Manager and SSH issue.  This issue is similar to HBASE-13330, except
this time the code path goes through ClosedRegionHandler and we should apply the same fix
of HBASE-13330 to ClosedRegionHandler.
> Basically, the AssignmentManager thinks the ServerShutdownHandler would assign the region
and the ServerShutdownHandler thinks that the AssignmentManager would assign the region. The
region (23e0186c4d2b5cc09f25de35fe174417) ultimately never gets assigned. Below is an analysis
from the logs that captures the flow of events.
> 1. The AssignmentManager had initially assigned this region to {{rs42.prod.foo.com,16020,1476293566365}}.
> 2. The {{rs42.prod.foo.com,16020,1476293566365}} stops and sends the CLOSE request to
> 3. ServerShutdownHandler(SSH) runs to assign this region to {{rs44.prod.foo.com,16020,1476294287692}},
but assign failed.
> 4. When the master restarted it did a scan of the meta to learn about the regions in
the cluster. It found this region still being assigned to
> {{rs42} from the meta record.
> 5. However, this {{rs42}} server was not alive anymore. So, the AssignmentManager queued
up a ServerShutdownHandling task for this (that asynchronously executes):
> 6. In the meantime, the AssignmentManager proceeded to read the RIT nodes from ZK. It
found this region as well is in RS_ZK_REGION_FAILED_OPEN in the {{rs44}} RS.
> 7. The region was moved to CLOSED state:
> {noformat}
> 2016-10-12 17:45:11,637 DEBUG [AM.ZK.Worker-pool2-t6] master.AssignmentManager: Handling
RS_ZK_REGION_FAILED_OPEN, server=rs44.prod.foo.com,16020,1476294287692, region=23e0186c4d2b5cc09f25de35fe174417,
current_state={23e0186c4d2b5cc09f25de35fe174417 state=PENDING_OPEN, ts=1476294311564, server=rs44.prod.foo.com,16020,1476294287692}
> 2016-10-12 17:45:11,637 INFO  [AM.ZK.Worker-pool2-t6] master.RegionStates: Transition
{23e0186c4d2b5cc09f25de35fe174417 state=PENDING_OPEN, ts=1476294311564, server=rs44.prod.foo.com,16020,1476294287692}
to {23e0186c4d2b5cc09f25de35fe174417 state=CLOSED, ts=1476294311637, server=rs44.prod.foo.com,16020,1476294287692}
> 2016-10-12 17:45:11,637 WARN  [AM.ZK.Worker-pool2-t6] master.RegionStates: 23e0186c4d2b5cc09f25de35fe174417
moved to CLOSED on rs44.prod.foo.com,16020,1476294287692, expected rs42.prod.foo.com,16020,1476293566365
> {noformat}
> 8. After that the AssignmentManager tried to assign it again. However, the assignment
didn't happen because the ServerShutdownHandling task queued earlier didn't yet execute:
> {noformat}
> 2016-10-12 17:45:11,637 DEBUG [AM.ZK.Worker-pool2-t6] master.AssignmentManager: Found
an existing plan for table1,3025965238305402_2,1468091325259.23e0186c4d2b5cc09f25de35fe174417.
destination server is rs44.prod.foo.com,16020,1476294287692 accepted as a dest server = false
> 2016-10-12 17:45:11,697 DEBUG [AM.ZK.Worker-pool2-t6] master.AssignmentManager: No previous
transition plan found (or ignoring an existing plan) for table1,3025965238305402_2,1468091325259.23e0186c4d2b5cc09f25de35fe174417.;
generated random plan=hri=table1,3025965238305402_2,1468091325259.23e0186c4d2b5cc09f25de35fe174417.,
src=, dest=rs28.prod.foo.com,16020,1476294291314; 10 (online=11) available servers, forceNewPlan=true
> 2016-10-12 17:45:11,697 DEBUG [AM.ZK.Worker-pool2-t6] handler.ClosedRegionHandler: Handling
CLOSED event for 23e0186c4d2b5cc09f25de35fe174417
> 2016-10-12 17:45:11,697 WARN  [AM.ZK.Worker-pool2-t6] master.RegionStates: 23e0186c4d2b5cc09f25de35fe174417
moved to CLOSED on rs44.prod.foo.com,16020,1476294287692, expected rs42.prod.foo.com,16020,1476293566365
> 2016-10-12 17:45:11,697 INFO  [AM.ZK.Worker-pool2-t6] master.AssignmentManager: Skip
assigning table1,3025965238305402_2,1468091325259.23e0186c4d2b5cc09f25de35fe174417., it's
host rs42.prod.foo.com,16020,1476293566365 is dead but not processed yet
> 2016-10-12 17:45:11,884 INFO  [MASTER_SERVER_OPERATIONS-server01:16000-3] master.RegionStates:
Transitioning {23e0186c4d2b5cc09f25de35fe174417 state=CLOSED, ts=1476294311697, server=rs44.prod.foo.com,16020,1476294287692}
will be handled by SSH for rs42.prod.foo.com,16020,1476293566365
> {noformat}
> 9. When the ServerShutdownHandling task reaches to this region, it also skipped the region
in question. This was because this region was in RIT, and the ServerShutdownHandling task
thinks that the AssignmentManager would assign it as part of handling the RIT nodes:
> {noformat}
> 2016-10-12 17:45:11,892 INFO  [MASTER_SERVER_OPERATIONS-server01:16000-3] handler.ServerShutdownHandler:
Skip assigning region in transition on other server{23e0186c4d2b5cc09f25de35fe174417 state=CLOSED,
ts=1476294311697, server=rs44.prod.foo.com,16020,1476294287692}
> {noformat}

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