Re: Synchronizing slots from primary to standby

On Thu, Feb 1, 2024 at 8:15 AM Euler Taveira <euler(at)eulerto(dot)com> wrote:
>
> On Mon, Jan 29, 2024, at 10:17 AM, Zhijie Hou (Fujitsu) wrote:
>
> Attach the V72-0001 which addressed above comments, other patches will be
> rebased and posted after pushing first patch. Thanks Shveta for helping address
> the comments.
>
>
> While working on another patch I noticed a new NOTICE message:
>
> NOTICE: changed the failover state of replication slot "foo" on publisher to false
>
> I wasn't paying much attention to this thread then I start reading the 2
> patches that was recently committed. The message above surprises me because
> pg_createsubscriber starts to emit this message. The reason is that it doesn't
> create the replication slot during the CREATE SUBSCRIPTION. Instead, it creates
> the replication slot with failover = false and no such option is informed
> during CREATE SUBSCRIPTION which means it uses the default value (failover =
> false). I expect that I don't see any message because it is *not* changing the
> behavior. I was wrong. It doesn't check the failover state on publisher, it
> just executes walrcv_alter_slot() and emits a message.
>
> IMO if we are changing an outstanding property on node A from node B, node B
> already knows (or might know) about that behavior change (because it is sending
> the command), however, node A doesn't (unless log_replication_commands = on --
> it is not the default).
>
> Do we really need this message as NOTICE?
>

The reason for adding this NOTICE was to keep it similar to other
Notice messages in these commands like create/drop slot. However, here
the difference is we may not have altered the slot as the property is
already the same as we want to set on the publisher. So, I am not sure
whether we should follow the existing behavior or just get rid of it.
And then do we remove similar NOTICE in AlterSubscription() as well?
Normally, I think NOTICE intends to let users know if we did anything
with slots while executing subscription commands. Does anyone else
have an opinion on this point?

A related point, I think we can avoid setting the 'failover' property
in ReplicationSlotAlter() if it is not changed, the advantage is we
will avoid saving slots. OTOH, this won't be a frequent operation so
we can leave it as it is as well.

--
With Regards,
Amit Kapila.