[HBASE-4899] Region would be assigned twice easily with continually killing server and moving region in testing environment

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.92.0
• Fix Version/s: 0.92.0
• Hadoop Flags: Reviewed
• Assignee: Chunhui Shen
• Reporter: Chunhui Shen
• Created: 30/Nov/11 05:58
• Updated: 20/Nov/15 11:53
• Resolved: 02/Dec/11 05:56

Description

Before assigning region in ServerShutdownHandler#process, it will check whether region is in RIT,
however, this checking doesn't work as the excepted in the following case:
1.move region A from server B to server C
2.kill server B
3.start server B immediately

Let's see what happen in the code for the above case

for step1:
1.1 server B close the region A,
1.2 master setOffline for region A,(AssignmentManager#setOffline:this.regions.remove(regionInfo))
1.3 server C start to open region A.(Not completed)
for step3:
master ServerShutdownHandler#process() for server B
{
..
splitlog()
...
List<RegionState> regionsInTransition =
        this.services.getAssignmentManager()
        .processServerShutdown(this.serverName);
...
Skip regions that were in transition unless CLOSING or PENDING_CLOSE
...
assign region
}

In fact, when running ServerShutdownHandler#process()#this.services.getAssignmentManager().processServerShutdown(this.serverName), region A is in RIT (step1.3 not completed), but the return List<RegionState> regionsInTransition doesn't contain it, because region A has removed from AssignmentManager.regions by AssignmentManager#setOffline in step 1.2
Therefore, region A will be assigned twice.

Actually, one server killed and started twice will also easily cause region assigned twice.
Exclude the above reason, another probability :
when execute ServerShutdownHandler#process()#MetaReader.getServerUserRegions ,region is included which is in RIT now.
But after completing MetaReader.getServerUserRegions, the region has been opened in other server and is not in RIT now.

In our testing environment where balancing,moving and killing are executed periodly, assigning region twice often happens, and it is hateful because it will affect other test cases.