Re: left-deep plans?

Tom Lane wrote:
> Yes, and it's been rejected.  The notion is obviously bogus; it amounts
> to assuming that every database is a star schema with only one core table.

Interesting; yes, I suppose that's true.

> Once we get into GEQO territory, we are using the left-deep-only
> heuristic because that's the only kind of plan GEQO can construct.
> But at that point you've already given up any notion of exhaustive
> search.

I think most applications would prefer an exhaustive, deterministic 
search of a subset of the search space over a non-exhaustive, 
non-deterministic search of the same subset, given approximately the 
same performance. In other words, if confining the search to left-deep 
plans allows people to use the normal planner in situations where they 
would normally be forced to use GEQO to get acceptable performance, I 
think that would be a win.

Speaking of which, why does GEQO restrict its search to left-deep plans 
only?

-Neil