Re: PoC plpgsql - possibility to force custom or generic plan

> >
> > Hmm. I think the core problem here is that we're trying to control
> > the plancache, which is a pretty much behind-the-scenes mechanism.
> > Except in the case of an explicit PREPARE, you can't even see from
> > SQL that the cache is being used, or when it's used. So part of what
> > needs to be thought about, if we use the GUC approach, is when the
> > GUC's value is consulted. If we don't do anything special then
> > the GUC(s) would be consulted when retrieving plans from the cache,
> > and changes in their values from one retrieval to the next might
> > cause funny behavior. Maybe the relevant settings need to be captured
> > when the plancache entry is made ... not sure.
>
> What sort of funny behavior are you concerned about? It seems likely
> to me that in most cases the GUC will have the same value every time
> through, but if it doesn't, I'm not sure why we'd need to use the old
> value rather than the current one. Indeed, if the user changes the
> GUC from "force custom" to "force generic" and reruns the function, we
> want the new value to take effect, lest a POLA violation occur.
>

good note - so changing this GUC on session level requires reset plan cache.

I am not against to GUC, and I am not against to PLpgSQL #option. Just, and
I am repeating (I am sorry) - these tools are not practical for usage in
PLpgSQL. There should be some block level possibility to do some setting.

Regards

Pavel

>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>