On Sat, Apr 09, 2005 at 12:00:56AM -0400, Tom Lane wrote: > 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 ...
Actually, if the remote database supported a way to get a rows estimate from the query passed to db_link, it would be trivial, since you'd just pass that back. In fact, having such a function (estimate_rows_for_sql(text)) would probably be very useful to functions that wanted to support returning a rows estimate. -- Jim C. Nasby, Database Consultant [EMAIL PROTECTED] Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?" ---------------------------(end of broadcast)--------------------------- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match