> * Backend should pass its version number, database encoding, 
> default client encoding, and possibly other data (any ideas?) to
> frontend during startup, to avoid need for explicit queries to get
> this info.  We could also consider eliminating SET commands sent by
> libpq in favor of adding variable settings to startup packet's
> PGOPTIONS field.  Ideally we could get back to the point where a
> standard connection startup takes only one packet in each
> direction.

How about a bitmap field of "additional features" supported by
client/backend that can be negotiated? (Doesn't have to be bitmap, of
course, but the idea..) That way the server (or client - doesn't matter
who goes first, I guess) could say "I support X and Y, but not Z and Q".
If the client supports both X and Y, both are enabled. If it supports
only X, then only X is enabled.

X and Y? Well, the first thing that comes to mind is SSL support. I'm
not sure if it's still that way, but at least it used to be a pretty
ugly kludge there with the connection being dropped and re-connected in
some cases. I also seem to recall there was some talk about on-wire
compression support - that would also be ideal for something like this.
I'm sure there can be more...

It should be easy to make it version-independent - just make both client
and server reject any "protocol features" that are unknown.


These are features that can be enabled/disabled in a backend/client of
the same version. It cannot (at least not easily) be handled with
protocol versioning, since you can have for example 7.4 with or without
SSL.


//Magnus

Mon, 10 Mar 2003 22:13:37 +0100
"Magnus Hagander" <mha@sollentuna.net>
Re: [INTERFACES] Roadmap for FE/BE protocol redesign
"Magnus Hagander" <mha@sollentuna.net> writes:
> X and Y? Well, the first thing that comes to mind is SSL support. I'm
> not sure if it's still that way, but at least it used to be a pretty
> ugly kludge there with the connection being dropped and re-connected in
> some cases.

SSL support is a bad example, since it would have to be negotiated long
before any more general-purpose negotiation could occur.  (You do want
the connection authentication exchange to happen under cover of SSL, no?)

ISTM most of the other features you might want to turn on and off can be
handled as SET commands: the client tries to SET a variable, the backend
either accepts it or returns an error.  No need for special protocol
support if you do it that way.  Can you point to any examples that have
to have a special protocol feature instead?

			regards, tom lane

Mon, 10 Mar 2003 16:26:24 -0500
Tom Lane <tgl@sss.pgh.pa.us>
Re: [INTERFACES] Roadmap for FE/BE protocol redesign 