Re: Libpq support to connect to standby server as priority

On 2020-Nov-24, Tom Lane wrote:

> I'm inclined to go ahead and commit the 0001 patch I posted at [1]
> (ie, change the implementation of GUC_REPORT to avoid intra-query
> reports), since that addresses a performance problem that's
> independent of the goal here.  The rest of this seems to still
> be in Greg's court.

Sounded a good idea to me.

> Has anyone got an opinion about the further improvement I suggested:
> 
> >> As it stands, 0001 reduces the ParameterStatus message traffic to
> >> at most one per GUC per query, but it doesn't attempt to eliminate
> >> duplicate ParameterStatus messages altogether.  We could do that
> >> as a pretty simple adjustment if we're willing to expend the storage
> >> to remember the last value sent to the client.  It might be worth
> >> doing, since for example the function-SET-clause case would typically
> >> lead to no net change in the GUC's value by the end of the query.
> 
> On reflection this seems worth doing, since excess client traffic
> is far from free.

Agreed.  If this is just a few hundred bytes of server-side local memory
per backend, it seems definitely worth it.