Karl Schnaitter <karlsch@gmail.com> writes:
> Of course, PG can't "support" indexing with incorrect functions. However,
> it's worthwhile to guard against too much damage being done if the user's
> function has a bug. Maybe I'm wrong? Maybe an index tuple with a dangling
> pointer is actually harmless?
No, it's far from harmless. As soon as that heap TID gets filled with
an unrelated tuple, you run the risk of indexscans alighting on and
perhaps modifying the wrong tuple.
regards, tom lane