>Do you need to plan for every combination, where some joins are removed >and some are not?
I would vote for just having two plans and one switch node. To exploit any finer grain, we'd have to have infrastructure that would let us figure out*which* constraints pending triggers might indicate transient invalidity of, and that doesn't seem likely to be worth the trouble.
In the interest of keeping the first pass simple... what if there was simply a switch node in front of every join that could be removable? That means you'd still be stuck with the overall plan you got from not removing anything, but simply eliminating the access to the relation(s) might be a big win in many cases, and presumably this would be a lot easier to code.
I can't quite get my head around what you mean here, as the idea sounds quite similar to something that's been discussed already and ruled out.
If we're joining relation a to relation b, say the plan chosen is a merge join. If we put some special node as the parent of the merge join then how will we know to skip or not skip any sorts that are there especially for the merge join, or perhaps the planner choose an index scan as a sorted path, where now that the join is removed, could become a faster seqscan. The whole plan switching node discussion came from this exact problem. Nobody seemed to like the non-optimal plan that was not properly optimised for having the relation removed.
It also seems that transitioning through needless nodes comes at a cost. This is why I quite liked the Alternative Plan node idea, as it allowed me to skip over the alternative plan node at plan initialisation.