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From "Ibrahim El-sanosi (PGR)" <i.s.el-san...@newcastle.ac.uk>
Subject Zab Failure scenario
Date Sun, 27 Sep 2015 15:51:08 GMT
Assume we use ZooKeeper 3.4.6 and we have 3-server cluster. Leader (L), follower1 (F1) and
follower2 (F2). The scenario is as following:

1.       Leader sends a proposal with Zxid = 10.

2.       F2 crashes before receiving P10. F1 logs, sends an ACK and crashes.
As there is no quorum  supporting L, L moves to LOOKING phase to find a quorum and elects
new leader. After sometime F1 wakes up and form a quorum with L.  Both F1 and L (pervious
leader) have same state (zxid =10 in their log). Therefore the process which has the large
myid will be a leader, assume L (pervious leader) has larger myid, So,

3.       L sends a pending proposal with Zxid =10 to F1.

4.       F1 logs and sends an ACK.

5.       Upon receiving ACK, L commits p10 and sends an ACK.



(1)    Is this true or false?

(2)    Regards,
Ibrahim


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