In the pluggable-storage discussion, there was some talk of renaming nodes/relation.h to avoid confusion with the new access/relation.h header. I think this is a fine idea, not only because of that conflict but because "relation.h" has never made a lot of sense as the file's name.
After a bit of thought, I propose "pathnodes.h" as the new name. That fits in with the other major headers in that directory (primnodes.h, parsenodes.h, plannodes.h, execnodes.h), and it seems like a reasonable summary of what's in it. Admittedly, Path nodes as such are barely a third of the file's bulk; but I don't see any equally pithy way to describe the rest of it, unless something like planner_data.h, which is pretty unmelodious. (There was some mention of trying to split relation.h into multiple files, but I fail to see any advantage in that.) Barring objections, I'm happy to go make this happen. regards, tom lane