Teodor Sigaev <teodor@sigaev.ru> writes:
>> operations such as page splits. Do we need to change the planner to
>> assume that this only works nicely for btree?
> It seems to that direction (backward or forward) has meaning only for
> indexes with amcanorder = true. With amcanorder=false results will be
> occasionally for any direction.
Well, no; amcanorder specifies that the index can return results that
are sorted according to some externally meaningful ordering. The
question at hand is just whether the results of a single indexscan
are self-consistent. That's a property that can reasonably be expected
to hold regardless of amcanorder; it does hold for hash indexes for
instance. (In the case of hash we have to forbid splitting a bucket
that's actively being scanned in order to make it true.)
regards, tom lane