Re: Views and functions returning sets of records

Giorgio Valoti <giorgio_v(at)mac(dot)com> writes:
> Are there any way to pass some hints to the planner? For example,
> could the IMMUTABLE/STABLE/VOLATILE modifiers be of some help?

Those don't really do anything for set-returning functions at the
moment.

As of 8.3 there is a ROWS attribute for SRFs that can help with one
of the worst problems, namely that the planner has no idea how many
rows a SRF might return. It's simplistic (just an integer constant
estimate) but better than no control at all.

As of CVS HEAD (8.4 to be) there's a capability in the planner to
"inline" SRFs that are single SELECTs in SQL language, which should
pretty much eliminate the performance differential against a comparable
view. Unfortunately 8.4 release is at least a year away, but just
so you know. (I suppose if you were desperate enough to run a privately
modified copy, that patch should drop into 8.3 easily enough.) IIRC
the restrictions for this to happen are
* single SELECT
* function declared to return set
* function NOT declared strict or volatile
* function NOT declared SECURITY DEFINER or given any
local parameter settings
The latter restrictions are needed so that inlining doesn't change
the semantics.

regards, tom lane