Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> [... thinks for awhile ...] It seems possible that they may use sort
>> code that knows it is performing a DISTINCT operation and discards
>> duplicates on sight. Given that there are only 534 distinct values,
>> the sort would easily stay in memory if that were happening.
> Could this optimization be added to PostgreSQL? It sounds like a very
> reasonable thing to do.
That's what I was wondering about too. But first I'd like to get
some kind of reading on how effective it would be. If someone can
demonstrate that Oracle can do sort-and-drop-dups a lot faster than
it can do a straight sort of the same amount of input data, that
would be a strong indication that it's worth doing. At this point
we don't know if that's the source of their win or not.
regards, tom lane