Re: Reversing flow of WAL shipping

Hi David,

On 22/10/2009, at 2:52 PM, David Jantzen wrote:
> I want to run a warm standby scenario by you. I'm pretty sure it'll
> work, but it's a very large database so even the slightest mistake can
> mean a major setback.
>
> Scenario:
>
> Server A is the provider node, shipping WAL files to Server B. Server
> B is destined to become the provider node (newer hardware), and has a
> sibling Server C that will be the warm standby.
>
> Here's the question: when I turn Server B into the production/provider
> node, it's going to switch into the next timeline. If I then attempt
> to put Server A (or Server C) into recovery mode, will it switch to
> the new current timeline, or complain about being in the older
> timeline? Do I have to take another full backup of Server B after
> it's become the production/provider node?

I did a similar trick more than once with a mission-critical database
by starting with 1 master/provider server (A) and 2 warm standby
servers (B, C), then failing over from A to B, then shipping WAL files
from the new master B to C. However I might be (ab)using the feature
or bug in Postgresql 8.0 that it wouldn't switch to a new timeline in
my environment. (I'd love to find out why it was so.) Please see http://archives.postgresql.org/pgsql-general/2009-07/msg00215.php
for details.

Yar