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From ms209495 <jezd...@gmail.com>
Subject Ensure there is one master
Date Tue, 26 Nov 2013 08:54:44 GMT

ZooKeeper is an excellent system but the problem with ensuring only one
master among clients bothers me.

Lets have a look at the situation when network partition happen: there is
part A (majority), and part B (minority).
Lets assume that before network partition happened the master was connected
to part B.
After the network partition, part A will elect new ZooKeeper leader, and
there will be new master elected among clients connected to part A.
At this time there are two masters - old in part B, and new in part A.
The only solution I can think about to this problem, is to ensure that the
new master is inactive for some time - to ensure that the old master in this
time will detect that it is not connected to ZooKeeper quorum, and will
deactivate itself as a master.
This solution assumes that timers on these machines work correctly.
Is it possible to ensure only one master using ZooKeeper without timing
assumptions ?


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