[pgpool-general: 2712] Re: Using one pgpoll instance per app server?

Tatsuo Ishii ishii at postgresql.org
Mon Apr 7 21:36:42 JST 2014

> Hello!
> I'm very new to pgpool, so please allow me to ask what is probably a
> newby question.
> I wish to use pgpool just for failover purposes: The DB loads are quite
> light, so a single DB server could easily handle them.
> However, I don't want pgpool to become a single point of failure. Please
> note that I won't be able to do virtual IP address failover in my
> particular server environment, so the usual approach (heartbeat + IP
> failover) won't be applicable here.
> Now I'm wondering whether I could just run one pgpool instance on each
> of my appservers (there are 2 or 3 of those), with each appserver
> connecting to their local pgpool instance. Each instance would be
> configured the same way: Using the same DB server as master, for
> example.
> Then, if one of my DB servers fails, each pgpool instance would
> eventually realize this and start to send their queries to the standby.
> However, if one of my pgpool or appserver instances fails, that
> appserver simply us out of rotation, which would be clean and neat.
> So, I guess it boils down to this question: Can I have multiple pgpool
> instances actively accessing the same database cluster (and the same
> database) at the same time?

Yes. Also I recommend to enable watchdog. In this case watchdog acts
as just a coordinator for same operations which need interlocking:
failover script and online recovery script.

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

> Thank you very much...
> Juergen
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