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From Ibrahim <i.s.el-san...@newcastle.ac.uk>
Subject New join server while leader just sends proposal?
Date Thu, 25 Dec 2014 21:20:20 GMT
I have a scenario where ZooKeeper ensemble consists of five physical servers
[A, B, C, D, E], assume C is the leader and all ZK servers have seen the
state [zxid=1, zxid=2, zxid=3, and zxid=4]. 

Now the leader broadcasts (send a proposal with zxid=5) to the followers.
Just after the leader sends proposal (before the proposal is committed), new
server (F) joins the cluster and it syncs with the leader (leader sends DIFF
to the F), so in this case, the server F will have state [zxid=1, zxid=2,
zxid=3, and zxid=4], but F has just missed the proposal zxid.

Now assume the proposal zxid is committed and delivered, resulting in
servers [A, B, C, D, E] have the state [zxid=1, zxid=2, zxid=3, zxid=4, and
zxid=5], whereas server F has only [zxid=1, zxid=2, zxid=3, and zxid=4] not
including zxid=5. 

This will end up the Zookeeper with inconsistent state at least for a short
time. 

Does this scenario correct (may happen)? If not how does Zookeeper deal with
such scenario?

Thank you
Ibrahim




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