Neil Conway <neilc@samurai.com> writes:
> BTW, I think it would make sense to implement a limited subset of the
> xfunc ideas: add options to CREATE FUNCTION to allow cost information to
> be specified, and then take advantage of this information instead of
> using the existing constant kludges. This would be a tangible
> improvement, and would have minimal impact on the planner.
The trick is to figure out what a useful parameterized cost model would
look like. IIRC, the main reason the xfunc code rotted on the vine was
that its cost parameters didn't seem to be either easy to select or
powerful in predicting actual cost. We'd have to do better this time.
regards, tom lane