Re: speed up a logical replica setup

On Thu, Jan 4, 2024, at 2:41 AM, Amit Kapila wrote:
> So, you also seem to be saying that it is not required once
> pg_subscriber has promoted it. So, why it should be optional to remove
> physical_replication_slot? I think we must remove it from the primary
> unless there is some other reason.

My point is to *always* remove the primary_slot_name on primary.

> My point is to not have an additional slot and keep a comment
> indicating that we need an extra slot once we add pg_basebackup
> support.

Got it.

> > 3. How about sync slots on the physical standby if present? Do we want
> > to retain those as it is or do we need to remove those? We are
> > actively working on the patch [1] for the same.
> >
> >
> > I didn't read the current version of the referred patch but if the proposal is
> > to synchronize logical replication slots iif you are using a physical
> > replication, as soon as pg_subscriber finishes the execution, there won't be
> > synchronization on these logical replication slots because there isn't a
> > physical replication anymore. If the goal is a promotion, the current behavior
> > is correct because the logical replica will retain WAL since it was converted.
> >
>
> I don't understand what you mean by promotion in this context. If
> users want to simply promote the standby then there is no need to do
> additional things that this tool is doing.

ENOCOFFEE. s/promotion/switchover/

> > However, if you are creating a logical replica, this WAL retention is not good
> > and the customer should eventually remove these logical replication slots on
> > the logical replica.
> >
>
> I think asking users to manually remove such slots won't be a good
> idea. We might want to either remove them by default or provide an
> option to the user.

Am I correct that the majority of the use cases these replication slots will be
useless? If so, let's remove them by default and add an option to control this
behavior (replication slot removal).

--
Euler Taveira
EDB https://www.enterprisedb.com/