Greg Stark <gsstark@mit.edu> writes:
> It's not a precise noop in database internal data structures, but I don't see
> any user-visible effects switching around seqnos would have. But maybe there's
> something I don't know about?
It'll affect the order in which pg_dump lists the parents, which will
affect the order in which the columns are created on dump and reload.
(Or at least it ought to ... right offhand I don't see anything in the
pg_dump source code that ensures the original order is preserved. This
may be a pg_dump bug.)
> I did wonder whether it was kosher to leave holes.
Not sure. I don't offhand see anything that requires the numbers to be
consecutive.
If you don't compact out the holes during DROP, then ADD could use the
rule of "first unused number" instead of max+1. This would ensure
DROP/ADD is a no-op for simple cases in which you only unlink from one
parent.
regards, tom lane