Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Nov 22, 2010 at 11:05 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I'm satisfied to say that only one sort order can be associated with a
>> particular operator in a particular opclass, which is what would be
>> implied by using AMOP_SEARCH/AMOP_ORDER as the unique key component.
> Does that imply that KNNGIST would only be able to support one
> ordering per AMOP_ORDER-operator, or does it imply that each such
> ordering would require a separate strategy number? The second might
> be OK, but the first sounds bad.
It would be the first, because simply assigning another strategy number
only satisfies one of the unique constraints on pg_amop. To allow
arbitrary flexibility here, we would have to include all components of
the ordering specification in the unique constraint that's presently
just (amopopr, amopfamily) and is proposed to become
(amopopr, amopfamily, amoppurpose). I think that's an undue amount of
complexity to support something that's most likely physically impossible
from the index's standpoint anyway.
regards, tom lane