Thanks Ibrahim for your explanation!
At 2014-11-05 19:48:20, "Ibrahim El-sanosi (PGR)" <[email protected]> wrote: >Hi bit1129, > >Yes you are right, when no majority is able to do the acknowledgement, they >will not be quorum in sync lists (followers and leader). So all members will >have "looking state" meaning that starting form new Zookeeper cluster. >Yes, it is similar to the case above. > >Thank you > >Ibrahim > >-----Original Message----- >From: Ibrahim El-sanosi (PGR) >Sent: Wednesday, November 05, 2014 11:34 ص >To: [email protected] >Subject: RE: RE: Question about ZAB > >Hi bit1129, > >Yes you are right, when no majority is able to do the acknowledgement, they >will not be quorum in sync lists (followers). So all members will have >"looking state" meaning that starting form new Zookeeper cluster. >Yes, it is similar to the case above. > >Thank you > >Ibrahim > >-----Original Message----- >From: [email protected] [mailto:[email protected]] >Sent: Wednesday, November 05, 2014 03:16 ص >To: dev >Subject: Re: RE: Question about ZAB > >Hi Ibrahim, >Thanks for the explaination. The last point makes sense to me that the >follower out of sync will be kicked out of the ensemble, and the follower will >have to rejoin(State syncronization happens after rejoining). > >For the case that no majority is able to do the acknowlegement, will the >leader simply declear the ensemble fails and can't work any more? I think >this is similar the the above case, that is, every follower will be kicked out >of the ensemble until there is no majority there? > >Thanks. > > > > > > >-Todd > >From: Ibrahim El-sanosi (PGR) >Date: 2014-11-05 10:34 >To: [email protected] >Subject: RE: Question about ZAB >Hi bit1129, > >* What does atomic in ZAB really mean? Does it mean that when the proposal >commits, it(including leader and follower) modifies the server state in an >atomic way? >It means all zookeeper server will commit the write transaction or none of >them does. (not 100% sure) > >* a. If no majority of followers acknowledge the proposal, then very likely >that the ensemble are in network issue or in chaos, then if this does happen, >how does the ensemble proceed? > >There is timeout for each write transaction, if the timeout elapse and the >majority does reach, simply the request will ignore (not deliver), the next >write request will start process. > >* If there is majority of followers that acknowledge the proposal and commit >the proposal, what about the othere followers that are not in this majority, >say, one is out of sync with the leader, what happens to this follower? >Will it sync with the leader to keep the state update? > >Assume we have 5 zookeeper servers (A, B, C, D, E) and A is a leader and the >other are follower. Now the write request comes to the leader, leader send a >proposal to the followers and itself. Let’s say A, B, C, D send ACK to the >leader but D does not. If the timeout elapse for D (for send ack), the leader >will drop D server from ensemble. Whenever the D join the Zookeeper, the >leader will send DIFF or snapshot to D making it in consistent state. It >sends DIFF or Snapshot, this depends on how far D is compared to A state. > >I hope this make sense to you > >Ibrahim >-----Original Message----- >From: [email protected] [mailto:[email protected]] >Sent: Wednesday, November 05, 2014 01:54 ص >To: dev >Subject: Question about ZAB > >Hi Zookeepers, >I got two questions that I am not certain about the behavior of ZAB, so I >would ask. > >1. What does atomic in ZAB really mean? Does it mean that when the proposal >commits, it(including leader and follower) modifies the server state in an >atomic way? >2.When a leader raises a proposal, and the followers ackownlege it, then the >leader broadcasts the commit message to let the followers to commit the >proposal.In this regulare process, there are two exceptional cases: > >a. If no majority of followers acknowledge the proposal, then very likely that >the ensemble are in network issue or in chaos, then if this does happen, how >does the ensemble proceed? >b. If there is majority of followers that acknowledge the proposal and commit >the proposal, what about the othere followers that are not in this majority, >say, one is out of sync with the leader, what happens to this follower? >Will it sync with the leader to keep the state update? > >Thanks! > > > > >-Todd
