Richard Huxton <dev@archonet.com> writes:
> Have you looked at marking f1() etc cachable? This means Postgresql
> will only call the function once for each parameter-set.
Unfortunately that's not true at all, or at least not helpful for this
problem. The cachable attribute was poorly named, because it leads
people to think that PG *will* cache function results, as opposed to
*could* cache function results.
A possible workaround is along the lines of
SELECT f1, f1 + f2, f1 + f2 + f3 FROM
(SELECT f1() as f1, f2() as f2, f3() as f3 LIMIT 1) tmp;
Note the LIMIT 1 ... without that, the planner may flatten the two
levels of SELECT together, eliminating the savings you're trying for.
(I don't recall offhand all the conditions that govern flattening
of a sub-select, but I'm pretty sure a sub-LIMIT will prevent it.)
regards, tom lane
