2011/2/22 Jody McIntyre <jodym@trustcentric.com>:
> On Mon, Feb 21, 2011 at 10:00 PM, Fujii Masao <masao.fujii@gmail.com> wrote:
>>
>> The resource agents for MySQL and DRBD have been implemented as
>> master/slave ones. So I think that the resource agent for PostgreSQL also
>> should be done the same way, i.e., you should implement only "start" and
>> "stop" but also "promote" and "demote".
>
> The trouble with postgres is there's no easy way to "demote" a master
> machine to a slave. You need to create a new master, back up its database,
> and restore it onto the slave before starting it. This seems difficult to
> implement, and pacemaker is already very complicated as it is.
>
> We are seriously considering writing our own tool that simply tests the
> master from the slave, and runs a very simple shell script to take over if
> necessary.
>
We have some work in progress in repmgr for that. And it offers
stronger choice when you have several standby and want to pick the
most up to date to become a new master.
--
Cédric Villemain 2ndQuadrant
http://2ndQuadrant.fr/ PostgreSQL : Expertise, Formation et Support