2. BCDE ack this proposal. BCDE must write the proposal to log before acknowledging the leader.
After CDE get restarted, they will re-apply the transaction in log so the committed transaction will be applied eventually. 2014-11-10 3:08 GMT-08:00 [email protected] <[email protected]>: > Thanks Eason, this makes sense, but the answer leads me for another > question. > > Say, A is the leader, BCDE are the followers, consider the following > scenario: > > 1. A sends a proposal to BCDE for a update. > 2. BCDE ack this proposal. > 3. A send the COMMIT request to BCDE. > 4. B commit the request, but CDE dont' because of power off before B > commits. > > At this point, A and B are alive but there is no majority any more, so the > zookeeper service is actually down. The user notices this and first shut > down A and B, and then restart CDEAB one by one. > > Because CDE don't have the latest update commit, is it the case that when > A and B startup ,their last committed update will be discarded? > > > > > > > > [email protected] > > From: Eason Liao > Date: 2014-11-10 18:41 > To: user > Subject: Re: How does Zookeeper handle this situation > It's possible that D, E have more recent data, and the data of D, E will be > discarded if they join leader. This is fine as long as the data is not > COMMITTED. > > We consider the transaction is committed only if the transaction is > persisted in the log of majority servers. In this case, if D, E have the > committed data, then at least > one of A, B, C will also have it. So the committed data won't get lost. > > Hope this answers your question. > > > > 2014-11-10 2:36 GMT-08:00 [email protected] <[email protected]>: > > > > > Hi zookeepers, > > > > I got a question about leader election during ensemble starts up. Say, > I > > got five servers, ABCDE, and start them one by one. > > According to the election algorithm, ABC forms the majority, and then a > > leader is elected among ABC. When D, E start up, they will follow the > > leader. What if D or E have more recent data among ABCDE? > > D,E's latest data will simply be discard? If this is case, this is a > > critical issue. > > > > Very likely that I missed something how leader election works during > > startup, any explanation on this? thinks. > > > > > > > > > > [email protected] > > >
