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From "ramkrishna.s.vasudevan (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-5094) The META can hold an entry for a region with a different server name from the one actually in the AssignmentManager thus making the region inaccessible.
Date Mon, 26 Dec 2011 08:41:31 GMT

     [ https://issues.apache.org/jira/browse/HBASE-5094?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

ramkrishna.s.vasudevan updated HBASE-5094:
------------------------------------------

    Description: 
R1 is reassigned to RS3 during RS1 shutdown, even though R1 was just assigned to RS2 by load
balancer. So .META. table indicated R1 is on RS3. Both RS2 and RS3 think they have R1. Later
when RS3 shutdown, R1 is reassigned to RS2. RS2 will indicate ALREADY_OPENED. Thus the region
is considered assigned to RS2 even though .META. indicates it is on RS3.



1) Region R1 - Assigned from RS1 to RS2.
2) RS1 goes down and ServerShutDownHandler.  ServerShutDwonHandler finds RS1 with R1 from
META as still META is not yet updated to RS2.
3) As RS1 goes down R1 is assigned from RS1 to RS3.  
4) RS3 goes down. ServerShutdownHandler processes R1 and tries to assign it to RS2.
5) RS2 says ALREADY_OPENED but META shows RS3.

I was able to reproduce the scenario.





  was:
R1 is reassigned to RS3 during RS1 shutdown, even though R1 was just assigned to RS2 by load
balancer. So .META. table indicated R1 is on RS3. Both RS2 and RS3 think they have R1. Later
when RS3 shutdown, R1 is reassigned to RS2. RS2 will indicate ALREADY_OPENED. Thus the region
is considered assigned to RS2 even though .META. indicates it is on RS3.

T1: Load balancer tried to move R1 from RS1 to RS2
. 2011-11-21 14:03:20,812 INFO org.apache.hadoop.hbase.master.HMaster: balance hri=tableXY,\xB8Q\xEB\x85\x1E\xB8Q\xDF,1321573099841.ee2e205a60f1bb06cc73bc9df06289df.,
src=skynet-1,60020,1321912978281, dest=skynet-4,60020,1321912999305

T2: RS1 shutdown. 2011-11-21 14:03:24,759 DEBUG org.apache.hadoop.hbase.master.ServerManager:
Added=skynet-1,60020,1321912978281 to dead servers, submitted shutdown handler to be executed,
root=false, meta=true

T3:R1 is opened on RS2. 2011-11-21 14:03:26,131 DEBUG org.apache.hadoop.hbase.master.handler.OpenedRegionHandler:
The master has opened the region tableXY,\xB8Q\xEB\x85\x1E\xB8Q\xDF,1321573099841.ee2e205a60f1bb06cc73bc9df06289df.
that was online on skynet-4,60020,1321912999305

T4: As part of RS1 shutdown handling, region reassignment starts. It uses the region location
captured at T2. 2011-11-21 14:03:26,152 INFO org.apache.hadoop.hbase.master.handler.ServerShutdownHandler:
Reassigning 32 region(s) that skynet-1,60020,1321912978281 was carrying (skipping 0 regions(s)
that are already in transition)

T5: R1 is assigned to RS3. 2011-11-21 14:03:27,404 DEBUG org.apache.hadoop.hbase.zookeeper.ZKUtil:
master:60000-0x133b84f9f490000 Retrieved 115 byte(s) of data from znode /hbase/unassigned/ee2e205a60f1bb06cc73bc9df06289df;
data=region=tableXY,\xB8Q\xEB\x85\x1E\xB8Q\xDF,1321573099841.ee2e205a60f1bb06cc73bc9df06289df.,
origin=skynet-3,60020,1321912991430, state=RS_ZK_REGION_OPENED

T6: RS3 shutdown. R1 is reassigned to RS2. 2011-11-21 14:03:37,899 DEBUG org.apache.hadoop.hbase.master.AssignmentManager:
ALREADY_OPENED region tableXY,\xB8Q\xEB\x85\x1E\xB8Q\xDF,1321573099841.ee2e205a60f1bb06cc73bc9df06289df.
to skynet-4,60020,1321912999305

>From AssignmentManager point of view, the R1 is assigned to RS2. The .META. table indicates
the location is RS3.



    
> The META can hold an entry for a region with a different server name from the one actually
in the AssignmentManager thus making the region inaccessible.
> --------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-5094
>                 URL: https://issues.apache.org/jira/browse/HBASE-5094
>             Project: HBase
>          Issue Type: Bug
>            Reporter: ramkrishna.s.vasudevan
>
> R1 is reassigned to RS3 during RS1 shutdown, even though R1 was just assigned to RS2
by load balancer. So .META. table indicated R1 is on RS3. Both RS2 and RS3 think they have
R1. Later when RS3 shutdown, R1 is reassigned to RS2. RS2 will indicate ALREADY_OPENED. Thus
the region is considered assigned to RS2 even though .META. indicates it is on RS3.
> 1) Region R1 - Assigned from RS1 to RS2.
> 2) RS1 goes down and ServerShutDownHandler.  ServerShutDwonHandler finds RS1 with R1
from META as still META is not yet updated to RS2.
> 3) As RS1 goes down R1 is assigned from RS1 to RS3.  
> 4) RS3 goes down. ServerShutdownHandler processes R1 and tries to assign it to RS2.
> 5) RS2 says ALREADY_OPENED but META shows RS3.
> I was able to reproduce the scenario.

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