Re: Function execution costs 'n all that

On Mon, 2007-01-15 at 10:51 -0800, Richard Troy wrote:
> I therefore propose that the engine evaluate -
> benchmark, if you will - all functions as they are ingested, or
> vacuum-like at some later date (when valid data for testing may exist),
> and assign a cost relative to what it already knows - the built-ins, for
> example.

That seems pretty unworkable. It is unsafe, for one: evaluating a
function may have side effects (inside or outside the database), so the
DBMS cannot just invoke user-defined functions at whim. Also, the
relationship between a function's arguments and its performance will
often be highly complex -- it would be very difficult, not too mention
computationally infeasible, to reconstruct that relationship
automatically, especially without any real knowledge about the
function's behavior.

-Neil