Re: how to switch old replication Master to new Standby after promoting old Standby

On Mon, Mar 14, 2016 at 6:54 PM, Shulgin, Oleksandr
<oleksandr(dot)shulgin(at)zalando(dot)de> wrote:
> On Mon, Mar 14, 2016 at 6:28 PM, John Lumby <johnlumby(at)hotmail(dot)com> wrote:
>> 1. shut down both new Master and intended-to-be-new-Standby
>> 2. on intended-to-be-new-Standby, remove the entire content of pg_xlog and
>> the global/pg_control
>> 3. from new Master , tar + scp the entire content of pg_xlog and the
>> global/pg_control to intended-to-be-new-Standby

This is not robust and will corrupt your standby. Just take the case
of a relation data block modified on the to-be-new standby, and not
replayed since the last checkpoint before WAL forked: data will be
corrupted. Inconsistent pg_clog will likely break things.

> That does seem like a very risky strategy to me. Have you taken a look at
> pg_rewind (which is now part of the distribution)?

pg_rewind has been designed for that, and ensures that the
soon-to-be-standby has a minimum recovery target sufficient. You had
better use it.
--
Michael