[Pacemaker] Postgresql streaming replication failover - RA needed

[Serge Dubrouski]

On Wed, Nov 16, 2011 at 12:55 PM, Attila Megyeri
<amegyeri at minerva-soft.com>wrote:

> Hi Florian,
>
> -----Original Message-----
> From: Florian Haas [mailto:florian at hastexo.com]
> Sent: 2011. november 16. 11:49
> To: The Pacemaker cluster resource manager
> Subject: Re: [Pacemaker] Postgresql streaming replication failover - RA
> needed
>
> Hi Attila,
>
> On 2011-11-16 10:27, Attila Megyeri wrote:
> > Hi All,
> >
> >
> >
> > We have a two-node postgresql 9.1 system configured using streaming
> > replicaiton(active/active with a read-only slave).
> >
> > We want to automate the failover process and I couldn't really find a
> > resource agent that could do the job.
>
> That is correct; the pgsql resource agent (unlike its mysql counterpart)
> does not support streaming replication. We've had a contributor submit a
> patch at one point, but it was somewhat ill-conceived and thus did not make
> it into the upstream repo. The relevant thread is here:
>
> http://lists.linux-ha.org/pipermail/linux-ha-dev/2011-February/018195.html
>
> Would you feel comfortable modifying the pgsql resource agent to support
> replication? If so, we could revisit this issue and potentially add
> streaming replication support to pgsql.
>
>
> Well I'm not sure I would be able to do that change. Failover is
> relatively easy to do but I really have no idea how to do the failback part.


And that's exactly the reason why I haven't implemented it yet. With the
current way how replication is done in PostgreSQL there is no easy way to
switch between roles, or at least I don't know about a such way.
Implementing just fail-over functionality by creating a trigger file on a
slave server in the case of failure on master side doesn't create a full
master-slave implementation in my opinion.


> I will definitively have to sort this out somehow, I am just unsure
> whether I will try to use the repmgr mentioned in the video, or pacemaker
> with some level of customization...
>
> Is the resource agent that you mentioned available somewhere?
>
> Thanks.
> Attila
>
>
>
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-- 
Serge Dubrouski.
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