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

On Fri, May 17, 2024 at 3:15 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> OK, so you made it so that compressed data is fully self-identifying.
> Hence, there's no need to worry if something gets changed: the
> receiver, if properly implemented, can't help but notice. The only
> downside that I can see to this design is that you only have one byte
> to identify the compression algorithm, but that doesn't actually seem
> like a real problem at all, because I expect the number of supported
> compression algorithms to grow very slowly. I think it would take
> centuries, possibly millenia, before we started to get short of
> identifiers. So, cool.
>
> But, in your system, how does the client ask the server to switch to a
> different compression algorithm, or to restart the compression stream?

I was leaving the details around triggering that for this conversation
and in that patch just designing the messages in a way that would
allow adding the reconfiguration/restarting to be easily added in a
backwards-compatible way in a future patch. I would imagine that an
explicit `ParameterSet` call that sets `_pq_.connection_compression`
(or whatever the implementation details turn out to be) would also
trigger a compressor restart, and when restarted it would pick an
algorithm/configuration based on the new value of the parameter rather
than the one used at connection establishment.

--
Jacob Burroughs | Staff Software Engineer
E: jburroughs(at)instructure(dot)com