[Pgpool-general] pgPool HA set up

[Guillaume Lelarge]

On Wed, 2011-10-05 at 11:44 +0100, Thom Brown wrote:
> On 5 October 2011 11:40, Guillaume Lelarge <guillaume at lelarge.info> wrote:
> > On Wed, 2011-10-05 at 12:22 +0200, Guillaume Lelarge wrote:
> >> On Wed, 2011-10-05 at 10:13 +0100, Thom Brown wrote:
> >> > On 5 October 2011 10:05, Guillaume Lelarge <guillaume at lelarge.info> wrote:
> >> > > On Wed, 2011-10-05 at 09:38 +0100, Thom Brown wrote:
> >> > >[...]
> >> > >> This seems like it should be a very common setup, so does pgPool have
> >> > >> provisioning for this, like having a 3rd pgPool to manage them
> >> > >> somehow?
> >> > >>
> >> > >
> >> > > No, it's not possible right now, and there's no discussion between
> >> > > developers to do something like this (at least on pgpool-hackers).
> >> >
> >> > So no-one has ever configured pgPool to have true HA?  Isn't there any
> >> > kind of black magick trickery one can do with the existing config
> >> > options to achieve this?
> >> >
> >>
> >> I guess true HA really depends on your context.
> >>
> >> Say we have two data centers (DC1 and DC2), two PostgreSQL servers (PG1
> >> and PG2), and two pgpool servers (PGP1 and PGP2). I would have all users
> >> access to the database through PGP1. Say that DC1 isn't available
> >> anymore, what I would do is change the IPVS so that all users go through
> >> PGP2, change PGP2 configuration so that it cannot access to PG1, and
> >> make sure that PG2 is the new master. Which of course is not automatic,
> >> there are a few steps that need manual work.
> >>
> >> But actually, what you are asking for is quite hard to have.
> 
> I understand that MySQL cluster suite (or whatever it's called) has a
> master controller which provides this somehow.
> 

Not sure how it works, but it would be interesting to know.

> >> > So in load balancing mode, is backend_*0 regarded by pgPool to be the
> >> > primary, or is pgPool clever and polls the servers to figure this out?
> >> >
> >>
> >> You mean, in master_slave mode. AFAIR, yes, it is. But I'll check.
> >>
> >
> > And I was wrong. At least when you first start pgpool.
> 
> How does it then know where to direct write queries to?
> 

At the beginning, it always sends the write queries to backend 0.


-- 
Guillaume
  http://blog.guillaume.lelarge.info
  http://www.dalibo.com