I wrote:
> Actually, after sleeping on it it seems like the obvious thing is
> to test "sslot1.nvalues * sslot2.nvalues", since the work we are
> thinking about saving scales as that product. But I'm not sure
> what threshold value to use if we do that. Maybe around 10000?
Or maybe better, since we are considering an O(m*n) algorithm
versus an O(m+n) one, we could check whether
sslot1.nvalues * sslot2.nvalues - (sslot1.nvalues + sslot2.nvalues)
exceeds some threshold. But that doesn't offer any insight into
just what the threshold should be, either.
regards, tom lane