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From "Karthik Ranganathan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2413) Master does not respect generation stamps, may result in meta getting permanently offlined
Date Thu, 08 Apr 2010 18:03:36 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12855052#action_12855052
] 

Karthik Ranganathan commented on HBASE-2413:
--------------------------------------------

<< A more involved soln. would have us run the code that is executed when znode expires
but then when znode actually expires, the code will be run again and we'd have to be careful
we recognized the difference between the two runs and not knock out a server that was legit.
>>

I was thinking of something like this, not sure how easily this would translate to code:

1. In the server restart and sending a new start code, we process the shutdown of the older
instance:

if (this.serverAddressToServerInfo.containsKey(hostAndPort)) {
     if(newStartCode > currentStartCode) {
        // process shutdown of current incarnation of RS
        // register new incarnation of RS
     }
}


2. On the znode expire path:

// znodeExpiredHostAndPort = ...
// znodeExpiredStartCode = ...
if(serverAddressToServerInfo.containsKey(znodeExpiredHostAndPort) && znodeExpiredStartCode
>= currentStartCode) {
  // process shutdown
} else {
  // no op - this should already have been handled
}


> Master does not respect generation stamps, may result in meta getting permanently offlined
> ------------------------------------------------------------------------------------------
>
>                 Key: HBASE-2413
>                 URL: https://issues.apache.org/jira/browse/HBASE-2413
>             Project: Hadoop HBase
>          Issue Type: Bug
>          Components: master
>    Affects Versions: 0.20.3
>            Reporter: Karthik Ranganathan
>            Assignee: stack
>         Attachments: newserver.txt
>
>
> This happens if the RS is restarted before the zk node expires. The sequence is as follows:
> 1. RS1 dies - lets say its server string was HOST1:PORT1:TS1
> 2. In a few seconds RS1 is restarted, it comes up as HOST1:PORT1:TS2 (TS2 is more recent
than TS1)
> 3. Master gets a start up message from RS1 with the server name as HOST1:PORT1:TS2
> 4. Master adds this as a new RS, tries to red
> ---- The master does not use the generation stamps to detect that RS1 has already restarted.
> ---- Also, if RS1 contained meta, master would try to go to HOST1:PORT1:TS1. It would
end up talking to HOST1:PORT1:TS2, which spews a bunch of not serving region exceptions.
> 5. zk node expires for HOST1:PORT1:TS1
> 6. Master tries to process shutdown for HOST1:PORT1:TS1 - this probably interferes with
HOST1:PORT1:TS2  and ends up somehow removing the reassign meta in the master's queue.
> ---- Meta never comes online and master continues logging the following exception indefinitely:
> 2010-04-06 11:02:23,988 DEBUG org.apache.hadoop.hbase.master.HMaster: Processing todo:
ProcessRegionClose of test1,7094000000,1270220428234, false, reassign: true
> 2010-04-06 11:02:23,988 DEBUG org.apache.hadoop.hbase.master.ProcessRegionClose$1: Exception
in RetryableMetaOperation:
> java.lang.NullPointerException
>         at org.apache.hadoop.hbase.master.RetryableMetaOperation.doWithRetries(RetryableMetaOperation.java:64)
>         at org.apache.hadoop.hbase.master.ProcessRegionClose.process(ProcessRegionClose.java:63)
>         at org.apache.hadoop.hbase.master.HMaster.processToDoQueue(HMaster.java:494)
>         at org.apache.hadoop.hbase.master.HMaster.run(HMaster.java:429)

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