Re: Optimizer questions

konstantin knizhnik <k.knizhnik@postgrespro.ru> writes:
> 1. The cost compared in grouping_planner doesn't take in account price of get_authorized_users - it is not changed
whenI am altering function cost. Is it correct behavior?
 

The general problem of accounting for tlist eval cost is not handled very
well now, but especially not with respect to the idea that different paths
might have different tlist costs.  I'm working on an upper-planner rewrite
which should make this better, or at least make it practical to make it
better.

In the meantime you can probably force things to work the way you want
by doing the sort/limit in a sub-select and evaluating the expensive
function only in the outer select.
        regards, tom lane