> In an environment with geqo_threshold=1 and join_collapse_limit=1, would
> the planner be GEQO exclusive (and syntactic)?
GEQO's only function, basically, is to search for the join order to use.
If you're constraining the join order completely with
join_collapse_limit=1 then forcing the GEQO path to be taken would just
add pointless overhead. (If it does anything at all ... I don't remember
the logic exactly but we might be bright enough not to bother with GEQO in
such a situation, regardless of geqo_threshold.)
regards, tom lane