Message-ID: <7389f3b042bed5d6b8fcf4cbf890fc932bc7963e.camel@cybertec.at>
Subject: Re: pg_rewind
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: soumik.bhattacharjee@kpn.com
Cc: pgsql-admin@lists.postgresql.org, pgsql-admin@postgresql.org
Date: Tue, 28 Jan 2020 09:48:09 +0100
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On Mon, 2020-01-27 at 16:01 +0000, soumik.bhattacharjee@kpn.com wrote:
> I set the "wal_log_hints = on" , but enabling this parameter "on" in new MASTER(old SLAVE) needs a restart--
> which I cannot do as all application transactions are going on there now.
> 
> Also I used pg_rewind in old MASTER(which now I want to make as new SLAVE) and it was successful,
> but this also needs restart of new MASTER(old SLAVE) which is again an issue.
> 
> Command used: ./pg_rewind -D $PGDATA --source-server='host=<IP Address> port=5432 user=postgres password=xxxx
> 
> Could you please suggest how to get this to work to keep the MASTER(old SLAVE) up & running and make the old MASTER(new SLAVE)

If you want to use "pg_rewind", you have to plan for that ahead of time
by either using data page checksums or enabling "wal_log_hints".

The first requires longer don time, the second a restart.
There is no way to do that retroactively.

Just use "pg_basebackup" to create a new standby, and enable
"wal_log_hints" next time you get a chance to restart.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com