[pgpool-hackers: 3381] Failover consensus on even number of nodes

[Tatsuo Ishii]

Hi Usama,

When number of Pgpool-II nodes is even, it seems consensus based
failover occurs if n/2 Pgpool-II agrees on the failure. For example,
if there are 4 nodes of Pgpool-II, 2 nodes agree on the failure,
failover occurs. Is there any reason behind this? I am asking because
it could easily lead to split brain, because 2 nodes could agree on
the failover while other 2 nodes disagree. Actually other HA software,
for example etcd, requires n/2+1 vote to gain consensus.

https://github.com/etcd-io/etcd/blob/master/Documentation/faq.md#what-is-failure-tolerance

With n/2+1 vote requirements, there's no possibility of split brain.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp