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
