[Pgpool-general] 3 Servers needed?

[Damian Lubosch]

Hi David!

David Boreham wrote:

> 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 ?
>

I'll use pgpool for replication since I need to define every table in
slony which seems to be a fatiguing task. I just want to replicate (or
better: mirror) whole database systems for hot-backup.

>> 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).
>

Yes, that's exactly what I tried. I run the first tests and it looks
very promising. Acutally it does exactly what I wanted it to do :-)

The only configuration differences between the two machines were, that
the "listen address" is the actual machine running pgpool. I left the
rest unchanged, i.e. "backend_host_name" and
"secondary_backend_host_name" are both the same on the two machines. I
hope that this is correct.




>> 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.
>
>

I will try to realize the actual switchover with ucarp, which watches
over two (or more) machines to be online (and manages their ip-addresses).


Thanks a lot,

Damian.