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From "Keith Turner (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-1277) Race condition between master and tserver when acquiring tserver lock
Date Tue, 16 Apr 2013 14:59:16 GMT


Keith Turner commented on ACCUMULO-1277:

bq. It seems like a lot of the locking complexity in Accumulo might be alleviated by upgrading
to the 3.4.x versions of zookeeper, which supports multi-operation transactions.

I have wanted to use that feature in the past.  Maybe we can bump the version for 1.6  I think
the zookeeper team is now recommending 3.4.5.
> Race condition between master and tserver when acquiring tserver lock
> ---------------------------------------------------------------------
>                 Key: ACCUMULO-1277
>                 URL:
>             Project: Accumulo
>          Issue Type: Bug
>          Components: master, tserver
>    Affects Versions: 1.5.0, 1.4.3
>            Reporter: Daniel P Truitt
>            Assignee: Keith Turner
> When restarting a stopped tserver, the following happens:
> The tserver (in TabletServer.announceExistence()) creates an entry in zookeeper at /accumulo/instance-id/tserver/host:port.
> This in turn triggers master to execute the call chain:
> LiveTServerSet.process(WatchedEvent)
> LiveTServerSet.scanServers()
> LiveTServerSet.checkServer(Set<TServerInstance>, Set<TServerInstance>, String,
> The checkServer() method checks to see if the ZooLock data has been created yet (if tserver
loses the race, it has not yet been created) causing master to then delete the tserver node.
> When the tserver attempts to create the ZooLock, the parent path no longer exists and
creating the lock fails.  Eventually the tserver will time out waiting to create the lock,
and fail to start.
> This problem is easier to reproduce in a smallish cluster using a single zookeeper node,
where there is more latency between the tserver and zookeeper than there is between the master
and zookeeper.
> This behavior was introduced in the fix for ACCUMULO-1049.

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