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From "Simon Wang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CURATOR-330) Need a way to handle connection lost while entering double barrier
Date Tue, 24 May 2016 20:41:13 GMT
Simon Wang created CURATOR-330:
----------------------------------

             Summary: Need a way to handle connection lost while entering double barrier
                 Key: CURATOR-330
                 URL: https://issues.apache.org/jira/browse/CURATOR-330
             Project: Apache Curator
          Issue Type: Improvement
          Components: Recipes
    Affects Versions: 2.10.0
            Reporter: Simon Wang


Here is the problem I’m meeting:

Assuming 3 node ensemble, my application has 3 clients and each one runs on same zk node (Client
1, 2 and 3). They use double barrier for coordination. 

Client 1 is entering the barrier and waiting for the other 2. Now the other 2 nodes are down
and then the ensemble gets crashed and the client 1 gets LostConnectionException from enter().
That’s expected.

After while the other 2 nodes come back,  all clients need to retry operation and reenter
the same barrier (It might become more complex if creating a new barrier). Here is the problem:

If the session for client 1 is still alive, Client 1 calling enter method will get NodeExistException
as the ephemeral node corresponding to that session is not deleted yet. 

I wonder in this case what should I do from application side? Or I’m thinking can we add
a mechanism to reenter the barrier but skip creating child node for this client if that exists?

I would like to open a Jira for this if required. 

Thanks,
Simon




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