Re: Remove Standby (SLAVE) from Primary (MASTER) - Postgres9.1

On Thu, Oct 27, 2016 at 10:27 AM, Scott Mead <scottm(at)openscg(dot)com> wrote:

>
>
> On 10/27/16 10:12 AM, Joanna Xu wrote:
> > We need to keep the data as it is so remving data fold is not feasible.
> > If I run "pg_ctl promote" on the slave to make it fail over, this will
> break the replication and then clean up the configuration related to
> replication. Any feedback?
>
> Just to [hopefully] clear up some of the confusion..
>
> Somewhere I saw you mention 9.1 . Since you're using 9.1, you won't
> have any replication slots in use, if you were using replication slots,
> then the master server could started to queue up WAL files waiting for
> that node to come back. This could cause you to run out of disk space.
> If you were using a replication slot, you would need to (after
> promotion) connect to the master and drop it:
> - SELECT * FROM pg_replication_slots;
> - SELECT pg_drop_replication_slot(slot_name);
>
> https://www.postgresql.org/docs/9.4/static/functions-admin.html#FUNCTIONS-
> REPLICATION
> https://www.postgresql.org/docs/9.4/static/catalog-pg-
> replication-slots.html
>
> Again, since you're on 9.1, this doesn't matter, BUT, it's important to
> keep in mind for the future.
>
> If you are using pure streaming replication, there is nothing that needs
> 'clean-up' on the master. Doing a promote will indeed do what you want
> to accomplish (NB: See below if you are also archiving your WAL).
>
> That being said, many setups of streaming will also include WAL
> (pg_xlog) archiving (check the archive_mode and archive_command in your
> postgresql.conf on the master). If you have configured archiving,
> chances are, you will have some sort of cleanup job on the slave that
> deals with old archived logs. You would either
>
> A. Want to stop archiving (for the node you are promoting)
> B. Ensure that cleanup is still taking place
>
> These steps are not done for you when you promote a slave, it's
> something that you need to deal with yourself.
>
> There is one other thing to keep in mind. If you are promoting a
> database, it's going to become read-write. I would make sure to either
> erect a firewall around the promoted slave or edit your pg_hba.conf file
> to reject traffic from your applications. If, for some reason your
> application were to connect, you could end up with a split-brain
> scenario which would mean that some of your data is in the old master
> and some is in the newly promoted slave. This can be very, very
> dangerous. As long as you exercise care, you will be fine, it's just an
> important point that I've seen haunt people in the past.
> > Thanks,
> > Joanna
> >
> > -----Original Message-----
> > From: Adrian Klaver [mailto:adrian(dot)klaver(at)aklaver(dot)com]
> > Sent: Wednesday, October 26, 2016 7:50 PM
> > To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>; Joanna Xu <
> Joanna(dot)Xu(at)amdocs(dot)com>
> > Cc: pgsql-general(at)postgresql(dot)org
> > Subject: Re: [GENERAL] Remove Standby (SLAVE) from Primary (MASTER) -
> Postgres9.1
> >
> > On 10/26/2016 04:43 PM, Michael Paquier wrote:
> >> On Wed, Oct 26, 2016 at 11:18 PM, Joanna Xu <Joanna(dot)Xu(at)amdocs(dot)com>
> wrote:
> >>> I’ve been looking for a procedure (step by step) on how to remove
> >>> Standby
> >>> (SLAVE) from Primary (MASTER) for Postgres9.1 in google and the
> >>> archived postings, but no luck.
> >> Standby and master servers are two separate Postgres instances. So if
> >> you would like to remove a standby from a cluster. You just need to
> >> basically stop it, then remove its data folder. And you are done.
> >> There is no complicated science here.
> > Not sure that is what OP wants. From the original post:
> >
> > " ...
> > 2. After the standby is removed from the primary, both of nodes
> > are in standalone configuration. "
> >
> >
> >
> > --
> > Adrian Klaver
> > adrian(dot)klaver(at)aklaver(dot)com
> >
> > This message and the information contained herein is proprietary and
> confidential and subject to the Amdocs policy statement,
> > you may review at http://www.amdocs.com/email_disclaimer.asp
> >
>
> --
> Scott Mead
> Sr. Architect
> OpenSCG
>
>
>
>
> --
> Sent via pgsql-general mailing list (pgsql-general(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-general
>

All you have to do on the slave is:

*sudo su postgres*
*touch /opt/postgres/9.1/data/trigger'*

Then the slave will go to standalone mode./
--
*Melvin Davidson*
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.