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

2017-09-05 19:38 GMT+02:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> > 2. what syntax we should to use (if we accept this feature)? There was
> not
> > another proposal if I remember well - The PRAGMA syntax is strong because
> > we can very well specify to range where the plans caching will be
> > explicitly controlled. It is well readable and static.
>
> The complaint I have about PRAGMA is that it's yet another syntax for
> accomplishing pretty much the same thing. If you don't like the GUC
> solution, we've already got the "comp_option" syntax for static options
> in plpgsql. Sure, that's not too pretty, but that's not a good reason
> to invent yet another way to do it.
>

comp_option has only function scope, what is too limited for this purpose.

I don't prefer GUC for this purpose because you need to do SET/RESET on two
places. With GUC the code can looks like:

PERFORM set_config('cachexx', 'off')
FOR r IN SELECT ...
LOOP
PERFORM set_config(' cachexx', 'on')
....
PERFORM set_config('cachexx', 'off')
END LOOP;
PERFORM set_config('cachexx', 'on');

The another reason for inventing PRAGMA syntax to PLpgSQL was support for
autonomous transaction and I am thinking so is good idea using same syntax
like PL/SQL does.

>
> regards, tom lane
>