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From Maciej SmoleĊ„ski <jezd...@gmail.com>
Subject Ensuring there is at most one master
Date Tue, 26 Nov 2013 14:34:40 GMT
Hi,

ZooKeeper is an excellent system. 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 ?

Thanks,
Maciej

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