Re: Add new protocol message to change GUCs for usage with future protocol-only GUCs

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Second, I don't really like the idea of selectively turning GUCs into
> protocol-managed parameters. I think there are a relatively small
> number of things that we'd ever want to manage on a protocol level,
> but this design would force us to make it work for any GUC whatsoever.

I'd not been following along for the last few days, but I agree that
we don't want to make it apply to any GUC at all.

> I think we should start by picking one or two protocol-managed
> parameters that we want to add, and then adding those in a way that is
> distinct from the GUC system. I don't think we should add an abstract
> system divorced from any particular application.

There is a lot of infrastructure we'll have to re-invent if
we make this completely independent of GUCs, notably:
* a way to establish the initial/default value
* a way to display the active value

So my thought was that this should be implemented as an (unchangeable)
flag bit for a GUC variable, GUC_PROTOCOL_ONLY or something like that,
and then we would refuse SQL-based set attempts on that. The behavior
would end up being very much like PGC_BACKEND variables, in that we
could allow all the existing setting methods to work to establish
a session's initial value; but after that, it can only change within
that session via a protocol message from the client. With that
rule, it's okay for the protocol message to be nontransactional since
there's no interaction with transactions.

regards, tom lane