Right now the server just detects that the zxid is wrong, and calls close on the client. The client logs: 15:01:47,593 - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1159] - Unable to read additional data from server sessionid 0x131962b00540000, likely server has closed socket, closing socket connection and attempting reconnect (branch 3.3.3)
I will poke around and see if I can figure out a nicer way to indicate this condition. The expired state is perfectly fine for me in my use case. C -----Original Message----- From: Patrick Hunt [mailto:[email protected]] Sent: Thursday, August 04, 2011 1:51 PM To: [email protected] Subject: Re: devops/admin/client question: What do you do when you rollback? On Thu, Aug 4, 2011 at 10:29 AM, Fournier, Camille F. <[email protected]> wrote: > 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. Hi Camille, there's a long standing jira on this: https://issues.apache.org/jira/browse/ZOOKEEPER-523 > 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. It seems reasonable that if the client connects to all servers in the ensemble (that it knows about) and sees that it's ahead of each one, it should consider the session expired (we could add a new state, but seems like just treating as expired with a good log message would be better from b/w compat standpoint). I can't recall, does the client have sufficient information to make this determination, or is the server just disconnecting? Patrick
