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Zookeeper >> mail # user >> devops/admin/client question: What do you do when you rollback?

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Re: devops/admin/client question: What do you do when you rollback?
Hi Camille,

Can you share the kind of problems you were facing on the servers that
forced you to rollback the cluster?


On Thu, Aug 4, 2011 at 1:29 PM, Fournier, Camille F. <

> We had an issue here the other day where the ZK servers were running
> poorly, and in an effort to get them healthy again we ended up rolling back
> the cluster state. While this was, in retrospect, not the right solution to
> the problem we were facing, it brought up another problem. Namely, that many
> of our clients couldn't reconnect with their sessions because their zxid was
> too high (expected), but that the error they got when trying to do that
> reconnection was just a vanilla disconnected error. The result was that most
> of our clients had to be bounced.
> Aside from trying hard to avoid ever rolling back the cluster state, does
> anyone have a way they deal with this situation if it occurs? Should we
> consider enhancing the error message to the client so we could track the
> fact that we were ahead of the quorum zxid and react sensibly? Alternately,
> since we were sending a sessionId along with the zxid, perhaps it would be
> nice to check to see if the sessionId exists before checking the zxid, which
> would send an expired state signal which my client code could handle
> cleanly.
> Any ideas or suggestions would be welcome.
> C