Not too many releases ago, there were several columns in pg_proc that were intended to support estimation of the runtime cost and number of result rows of set-returning functions. I believe in fact that these were the remains of Joe Hellerstein's thesis on expensive-function evaluation, and are exactly what he was talking about here: http://archives.postgresql.org/pgsql-hackers/2002-06/msg00085.php
But with all due respect to Joe, I think the reason that stuff got trimmed is that it didn't work very well. In most cases it's *hard* to write an estimator for a SRF. Let's see you produce one for dblink() for instance ... regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings