Re: knngist - 0.8

On Mon, Nov 22, 2010 at 8:32 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The reason I bring this up now is that it affects the decision as to
> what the unique key for pg_amop ought to be.  Instead of having an
> enum "purpose" column, maybe we should consider that the unique key
> is (operator oid, opfamily oid, order-by-oid), where order-by-oid
> is zero for a search operator and the OID of the btree opclass or sort
> operator for an ordering operator.  This would be of value if we
> imagined that a single opclass could support ordering by more than one
> distance ordering operator; which seems a bit far-fetched but perhaps
> not impossible.  On the other side of the coin it'd mean we aren't
> leaving room for other sorts of operator "purposes".

Since the need for additional purposes is mostly hypothetical, this
wouldn't bother me any.

> On balance I'm inclined to leave the unique key as per previous proposal
> (with a "purpose" column) and add the which-sort-order-is-that
> information as payload columns that aren't part of the key.

This is probably OK too, although I confess I'm a lot less happy about
it now that you've pointed out the need for those payload columns.

-- 
Robert Haas
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