[pgpool-general: 2717] Re: Using one pgpoll instance per app server?

Juergen Brendel juergen at brendel.com
Tue Apr 8 04:27:51 JST 2014


Thank you for your reply...

On Mon, 2014-04-07 at 21:36 +0900, Tatsuo Ishii wrote:
> > 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.

I guess I don't understand the need for watchdog. My hope was that each
pgpool instance would independently be able to figure out that the
master DB had failed and would start to use the slave DB instead. Is
that not the case?

To clarify, the suggested architecture is like this:

           +---- appserver 1 --- pgpool 1 ---+
           |                                 +--- Master DB
    LB ----+---- appserver 2 --- pgpool 2 ---+
           |                                 +--- Slave DB
           +---- appserver 3 --- pgpool 3 ---+

Where "appserver 1" is on the same machine as "pgpool 1", "appserver 2"
on the same as "pgpool 2", and so on.

If the master DB fails, should not all pgpool instances independently
from each other detect this and switch over to the slave DB? What would
I need to use watchdog for?

Now imagine that replication between master and slave DB is handled by
those pgpool instances as well. Would this still be possible?

Thank you again...


More information about the pgpool-general mailing list