I wrote:
> Hm. In principle, add_path_precheck shouldn't be doing anything except
> rejecting paths that would get rejected anyway later on. However it
> strikes me that there's a logic error in it; specifically, this
> simplifying assumption is wrong:
> * For speed, we make exact rather than fuzzy cost comparisons. If an
> * old path dominates the new path exactly on both costs, it will
> * surely do so fuzzily.
After staring at this awhile longer, I still don't see exactly why it's
changing the results. Do we have instructions around here anyplace on
how to set up/use TPC-DS? I couldn't find anything about it on the
wiki ...
regards, tom lane