Re: Add ALL_CANDIDATES option to EXPLAIN

Anthonin Bonnefoy <anthonin(dot)bonnefoy(at)datadoghq(dot)com> writes:
> I have a prototype for an ALL_CANDIDATES option for EXPLAIN. The goal
> of this option is to print all plan candidates instead of only the
> cheapest plan. It will output the plans from the most expensive at the
> top to the cheapest.

This doesn't seem feasible at all to me. If we don't prune plans
fairly aggressively at lower plan levels, we'll have a combinatorial
explosion in the amount of work the planner has to do. Have you
tried this on even slightly complex plans --- say, a dozen-way join?
I do not think you'll like the runtime, the amount of memory consumed,
or the verboseness of the output. (I wonder how it interacts with
GEQO, too.)

regards, tom lane