[Pgpool-general] 3 Servers needed?

[David Boreham]

Damian Lubosch wrote:

> I am about to set up a postgresql replication system and would like to 
> try out pgpool.

Are you using slony or pgpool for replication ?

> But I couldn't find anywhere one important information:
> Do I need a seperate machine to run pgpool? Or is it possible to run 
> it on both - the primary and secondary pgsql machine?

I think the most obvious place to run pgpool is on every _client_ machine
(where client might be some mid-tier thing, rather than an end-user client).
The reason being that it's the clients of the database that you want to
protect from database failure. Hence you run pgpool locally on those
machines (on the basis that if the local machine is available, then so
is pgpool).

> I mean in case of a total failure of one machine the switchover has to 
> be managed somehow. So if the primary pgsql server goes down (with its 
> pgpool) is it possible that a (second running) pgpool instance on the 
> secondary server takes over?

This is why I think you should run pgpool on each client machine.
Then the switchover of pgpool does not need to happen : every
machine has its (hopefully working) copy of pgpool.