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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6060) Regions's in OPENING state from failed regionservers takes a long time to recover
Date Fri, 01 Jun 2012 18:06:24 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13287568#comment-13287568
] 

ramkrishna.s.vasudevan commented on HBASE-6060:
-----------------------------------------------

@Ted
bq.why cannot we return null above so that we don't need to add the boolean member to RegionPlan
?
The reason here is incase of null region plan we have a different behaviour.  We consider
it as a case where we dont have any live RS and hence set some flag such that the timeoutmonitor
can be skipped. Hence we need to differentiate the null behaviour from this.
{code}
if (plan == null) {
        LOG.debug("Unable to determine a plan to assign " + state);
        this.timeoutMonitor.setAllRegionServersOffline(true);
        return; // Should get reassigned later when RIT times out.
      }
{code}
I was not sure of which name to give for the usePlan.  May be 'usable' is better.
{code}
Before making the deadServerRegionsFromRegionPlan.put() call
{code}
I think as the SSH calls per server it should be ok. 
I will check on other comments before changing it. Thanks for your detailed review.
                
> Regions's in OPENING state from failed regionservers takes a long time to recover
> ---------------------------------------------------------------------------------
>
>                 Key: HBASE-6060
>                 URL: https://issues.apache.org/jira/browse/HBASE-6060
>             Project: HBase
>          Issue Type: Bug
>          Components: master, regionserver
>            Reporter: Enis Soztutar
>            Assignee: Enis Soztutar
>         Attachments: HBASE-6060-94.patch
>
>
> we have seen a pattern in tests, that the regions are stuck in OPENING state for a very
long time when the region server who is opening the region fails. My understanding of the
process: 
>  
>  - master calls rs to open the region. If rs is offline, a new plan is generated (a new
rs is chosen). RegionState is set to PENDING_OPEN (only in master memory, zk still shows OFFLINE).
See HRegionServer.openRegion(), HMaster.assign()
>  - RegionServer, starts opening a region, changes the state in znode. But that znode
is not ephemeral. (see ZkAssign)
>  - Rs transitions zk node from OFFLINE to OPENING. See OpenRegionHandler.process()
>  - rs then opens the region, and changes znode from OPENING to OPENED
>  - when rs is killed between OPENING and OPENED states, then zk shows OPENING state,
and the master just waits for rs to change the region state, but since rs is down, that wont
happen. 
>  - There is a AssignmentManager.TimeoutMonitor, which does exactly guard against these
kind of conditions. It periodically checks (every 10 sec by default) the regions in transition
to see whether they timedout (hbase.master.assignment.timeoutmonitor.timeout). Default timeout
is 30 min, which explains what you and I are seeing. 
>  - ServerShutdownHandler in Master does not reassign regions in OPENING state, although
it handles other states. 
> Lowering that threshold from the configuration is one option, but still I think we can
do better. 
> Will investigate more. 

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