Обсуждение: pg_rewind

On Thu, 2020-01-23 at 15:39 +0000, soumik.bhattacharjee@kpn.com wrote:
> I am trying to make my previous Master as Master by roll backing the changes happen into Standby
> 
> In Original MASTER I am running below –
> 
> /usr/lib/postgresql/12/bin$ ./pg_rewind -D $PGDATA --source-server='host=<IP Address> port=5432' -P
> pg_rewind: fatal: could not connect to server: fe_sendauth: no password supplied
> 
> I'm not sure why this keeps happening.

Because you used the wrong user or didn't specify a password?

Try

   --source-server='host=<IP Address> port=5432 user=... password=...'

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

Thanks for your suggestion, I need now to make "wal_log_hints = on"

-----Original Message-----
From: Laurenz Albe <laurenz.albe@cybertec.at> 
Sent: donderdag 23 januari 2020 16:56
To: Bhattacharjee, Soumik <soumik.bhattacharjee@kpn.com>; pgsql-admin@lists.postgresql.org; pgsql-admin@postgresql.org
Subject: Re: pg_rewind

On Thu, 2020-01-23 at 15:39 +0000, soumik.bhattacharjee@kpn.com wrote:
> I am trying to make my previous Master as Master by roll backing the changes happen into Standby
> 
> In Original MASTER I am running below –
> 
> /usr/lib/postgresql/12/bin$ ./pg_rewind -D $PGDATA --source-server='host=<IP Address> port=5432' -P
> pg_rewind: fatal: could not connect to server: fe_sendauth: no password supplied
> 
> I'm not sure why this keeps happening.

Because you used the wrong user or didn't specify a password?

Try

   --source-server='host=<IP Address> port=5432 user=... password=...'



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

-----Original Message-----
From: Laurenz Albe <laurenz.albe@cybertec.at> 
Sent: donderdag 23 januari 2020 16:56
To: Bhattacharjee, Soumik <soumik.bhattacharjee@kpn.com>; pgsql-admin@lists.postgresql.org; pgsql-admin@postgresql.org
Subject: Re: pg_rewind


> 
> In Original MASTER I am running below –
> 
> /usr/lib/postgresql/12/bin$ ./pg_rewind -D $PGDATA --source-server='host=<IP Address> port=5432' -P
> pg_rewind: fatal: could not connect to server: fe_sendauth: no password supplied
> 
> I'm not sure why this keeps happening.

Because you used the wrong user or didn't specify a password?

Try

   --source-server='host=<IP Address> port=5432 user=... password=...'


-- 
Thanks for your suggestion, I made the "wal_log_hints = on".

I set the "wal_log_hints = on" , but enabling this parameter "on" in new MASTER(old SLAVE) needs a restart-- which I
cannotdo 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
restartof 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)

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(newSLAVE)
 

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