Re: [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.

On Mon, Apr 10, 2017 at 5:47 PM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> Based on that we seem to agree here, should we add this as an open item?
> Clearly if we want to change this, we should do so before 10.

This really is a new feature, so as the focus is to stabilize things I
think that we should not make the code more complicated because...

> I also came up with another case where the current one won't work but it
> could be really useful -- if we make a replication connection (with say
> pg_receivewal) it would be good to be able to say "i want the master" (or "i
> want a standby") the same way. And that will fail today if it needs SHOW to
> work, right?
>
> So having it send that information across in the startup package when
> talking to a 10 server, but falling back to using SHOW if talking to an
> earlier server, would make a lot of sense I think.

Of this reason, as libpq needs to be compliant with past server
versions as well we are never going to save a set of version-dependent
if/else code to handle target_session_attrs properly using either a
SHOW or a new mechanism.
--
Michael