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From: rammohan ganapavarapu <rammohanganap(at)gmail(dot)com>
To: gparc(at)free(dot)fr, pgsql-admin(at)postgresql(dot)org
Date: 11/20/2017 01:25 PM
Subject: Re: [ADMIN] Can master and slave on different PG versions?

Gilles,

Thank you, if we set wal_level in version <= 9.6 to "logical" what does
it mean what does it do? do we still call it as logical replication? also
how to tell if my replication is logical or physical. Please excuse me if
i am asking stupid questions :) i am new to Postgres.

Ram

On Mon, Nov 20, 2017 at 2:20 AM, <gparc(at)free(dot)fr> wrote:

Hello,

yes, before postgres version 10, you must use an extension such as
pg_logical
to build logical replication between master and slave.

For pg_logical, see the following links to help you start :
https://www.2ndquadrant.com/en/resources/pglogical/pglogical-docs/
http://bonesmoses.org/2016/10/14/pg-phriday-perfectly-logical/
https://www.depesz.com/2016/11/08/major-version-upgrading-with-minimal-downtime/

Regards
Gilles

----- Mail original -----
De: "rammohan ganapavarapu" <rammohanganap(at)gmail(dot)com>
À: gparc(at)free(dot)fr, pgsql-admin(at)postgresql(dot)org
Envoyé: Vendredi 17 Novembre 2017 16:43:57
Objet: Re: [ADMIN] Can master and slave on different PG versions?

Hi,

I was using pg_basebackup to rebuild slave, so pglogical is not in-built
in postgres and I have to install?

Thanks

On Nov 17, 2017 12:42 AM, < gparc(at)free(dot)fr > wrote:

Hello,

How did you create the slave ? with pg_basebackup or via rsync ?
In any case, the slave MUST have been built with a backup/rsync made AFTER
the master have been restarted when you changed
wal_level to logical.

Note, that you did so far, set wal_level=logical, is just a prerequisite
to use logical replication.
After that, you need a tool which will extract the changes in the WALs
from the master and will replay them on the slave.

Such tool is pg_logical :
https://www.2ndquadrant.com/en/resources/pglogical/

Regards

----- Mail original -----
De: "rammohan ganapavarapu" < rammohanganap(at)gmail(dot)com >
À: gparc(at)free(dot)fr , pgsql-admin(at)postgresql(dot)org
Envoyé: Jeudi 16 Novembre 2017 17:58:42

Objet: Re: [ADMIN] Can master and slave on different PG versions?

From Slave (9.6):

Database cluster state: shut down in recovery

wal_level setting: logical

From master (9.4) :

Database cluster state: in production

Current wal_level setting: logical

Quite frankly i couldn't find proper document on how to set logical
replication in 9.4, i think i am using pg_logical. All i did was set
wal_level to logical and add primary_slot_name in recovery.conf. Do i need
to install pglogical extension? i couldn't find one for amazon linux.

Thanks,
Ram

On Thu, Nov 16, 2017 at 6:12 AM, < gparc(at)free(dot)fr > wrote:

Hello again,

can you execute pg_controldata command on both Master and Slave
and check the following properties :
Database cluster state
wal_level setting

Also, if I understand correctly, you want to establish logical replication
between your 9.4 master
and your 9.6 slave but you don't explain how ? using pg_logical ?

Regards

----- Mail original -----
De: "rammohan ganapavarapu" < rammohanganap(at)gmail(dot)com >
À: "David G. Johnston" < david(dot)g(dot)johnston(at)gmail(dot)com >
Cc: pgsql-admin(at)postgresql(dot)org
Envoyé: Mercredi 15 Novembre 2017 22:23:57
Objet: Re: [ADMIN] Can master and slave on different PG versions?

Any one tried this before?

On Wed, Nov 8, 2017 at 8:17 AM, rammohan ganapavarapu <
rammohanganap(at)gmail(dot)com > wrote:

David,

So initially i have physical replication configured, so to upgrade slave
to 9.6 version i did converted master slave to logical replication and
then try to upgrade the slave to 9.6. I am getting this error when i try
to start the slave. Any idea?

2017-11-08 05:08:49 UTC [20063]: [1-1] user= db= host= LOG: shutting down
2017-11-08 05:08:49 UTC [20063]: [2-1] user= db= host= LOG: database
system is shut down
2017-11-08 05:09:45 UTC [20322]: [1-1] user= db= host= LOG: database
system was shut down at 2017-11-08 05:08:55 UTC
2017-11-08 05:09:45 UTC [20322]: [2-1] user= db= host= LOG: entering
standby mode
2017-11-08 05:09:45 UTC [20322]: [3-1] user= db= host= WARNING: WAL was
generated with wal_level=minimal, data may be missing
2017-11-08 05:09:45 UTC [20322]: [4-1] user= db= host= HINT: This happens
if you temporarily set wal_level=minimal without taking a new base backup.
2017-11-08 05:09:45 UTC [20322]: [5-1] user= db= host= FATAL: hot standby
is not possible because wal_level was not set to "replica" or higher on
the master server
2017-11-08 05:09:45 UTC [20322]: [6-1] user= db= host= HINT: Either set
wal_level to "replica" on the master, or turn off hot_standby here.
2017-11-08 05:09:45 UTC [20312]: [3-1] user= db= host= LOG: startup
process (PID 20322) exited with exit code 1
2017-11-08 05:09:45 UTC [20312]: [4-1] user= db= host= LOG: aborting
startup due to startup process failure
2017-11-08 05:09:45 UTC [20312]: [5-1] user= db= host= LOG: database
system is shut down

Thanks,
Ram

On Mon, Oct 9, 2017 at 4:15 PM, David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com > wrote:

On Mon, Oct 9, 2017 at 4:06 PM, rammohan ganapavarapu <
rammohanganap(at)gmail(dot)com > wrote:

Hi,

Is it possible to add 9.6 version Slave to 9.4 master?

​Physical replication, no; Logical replication, yes - if the software you
are using is compatible with both versions.

David J.​