[Pgpool-general] pgPool HA set up

[Thom Brown]

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.

>> > 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?

Thom