Hi Rakesh, Thanks for your great explanation. That is what I wanted to know.
Regards, Imesha Sudasingha On 6 October 2016 at 12:25, Rakesh Radhakrishnan <[email protected]> wrote: > Hi Imesha Sudasingha, > > For example, we have A,B,C,D,E five servers, that formed quorum and assume > A is the Leader. Again assume network partition happened between > A,B(minority region) and C,D,E. As we know, 3 is the majority factor to > form quorum. Since Leader A is in the minority region, the entire quorum > will get shutdown and all the servers will automatically moves to leader > election phase. Now, A & B will do sending notifications each other and > will never succeed to form quorum due to <3 factor. On the other side, C,D > and E will participate each other and elect one of them as Leader. > > >>>>>But will the partition with a minority will also continue to serve > read > >>>>>requests until a write request comes to the leader in the minority > >>>>>partition? > After the partition, all the servers in the minority region will get > shutdown and moves to leader election phase. All the client sessions > connected to these servers will be disconnected and > will receive "KeeperState.Disconnected" event to their watchers, if any > registered. > > But ZooKeeper supports read-only server mode. In this mode, client can > connect to the read-only server even when the server might be partitioned > from the quorum. > > Reference:- Please read the section "Read Only Mode Server" in the apache > document link, https://zookeeper.apache.org/doc/r3.4.9/zookeeperAdmin.html > > > >>>>>In the above scenario, what will happen to the "watches" that have > >>>>>already been registered to a node in the minority partition? > Since the quorum is re-forming, all the client session watchers will > receive "KeeperState.Disconnected" event. These client session will start > sending connection request to all quorum servers(A,B,C,D,E) to re-establish > the connection. In my above example, C,D,E re-forms quorum successfully and > client sessions will reconnect to one of these servers in the quorum(am > assuming zkclient has the C,D,E server host address configured). Clients > automatically reset watches during successful session reconnect. There is a > feature to disable this watch resetting, please read the configuration > "zookeeper.disableAutoWatchReset" section in the following apache doc link > to understand more on this, > https://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html > > Regards, > Rakesh > > On Wed, Oct 5, 2016 at 6:39 PM, Imesha Sudasingha <[email protected] > > > wrote: > > > Hi all, > > > > When I was going through zookeeper, I noticed the following scenarios, > > > > - Suppose we have a 5 member quorum operating as normal. In a network > > partitioning where the leader and a member node goes into one > partition > > and > > other 3 nodes get into the other network partition. I known then the > > side > > with the majority will elect a new leader and carry on to serve > > requests. > > But will the partition with a minority will also continue to serve > read > > requests until a write request comes to the leader in the minority > > partition? How does zookeeper handle this occasion? > > - In the above scenario, what will happen to the "watches" that have > > already been registered to a node in the minority partition? > > > > Can you clarify the above scenarios? > > Thanks in advance! > > > > -- > > *Imesha Sudasingha* > > Undergraduate of Department of Computer Science and Engineering, > > University of Moratuwa. > > +94717086160 > > View in Linkedin <https://lk.linkedin.com/in/imeshasudasingha> > > > -- *Imesha Sudasingha* Undergraduate of Department of Computer Science and Engineering, University of Moratuwa. +94717086160 View in Linkedin <https://lk.linkedin.com/in/imeshasudasingha>
