Re: Hot Standby Failover Scenario

On 02/27/2012 10:05 PM, Lucky Haryadi wrote:
> 3. When Master A fails to service, the database will failovered to Slave
> B by triggering with trigger file.

As soon as you trigger a standby, it changes it to a new timeline. At
that point, the series of WAL files diverges. It's no longer possible
to apply them to a system that is still on the original timeline, such
as your original master A in this situation. There's a good reason for
that. Let's say that A committed an additional transaction before it
went down, but that commit wasn't replicated to B. You can't just move
records from B over anymore in that case. The only way to make sure A
is in sync again is to do a new base backup, which you can potentially
accelerate using rsync to only copy what has changed. I see a lot of
people try to bypass one of the steps recommended in the manual using
various schemes like yours, and they usually have a bug like this in
there--sometimes obvious like this, sometimes subtle. Trying to get too
clever here is dangerous to your database.

Warning: pgsql-hackers is the mailing list for people to discuss the
development of PostgreSQL, not how to use it. Questions like this
should be asked on either the pgsql-admin or pgsql-general mailing list.
I'm not going to answer additional questions like this from you here
on this list, and I doubt anyone else will either.

--
Greg Smith 2ndQuadrant US greg(at)2ndQuadrant(dot)com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com