Re: EXPLAIN ANALYZE output weird for Top-N Sort

On 14/11/14 14:54, Tom Lane wrote:
> Jeremy Harris  writes:
>> On 14/11/14 00:46, Simon Riggs wrote:
>>> Limit  (cost=.... rows=20 width=175) (actual time=.... rows=20 loops=1)
>>> ->  Sort  (cost=.... rows=568733 width=175) (actual time=....
>>> rows=20 loops=1)
>>> Sort Method: top-N heapsort
> 
>> Going off on a tangent, when I was playing with a merge-sort
>> implementation I propagated limit information into the sort
>> node, for a significant win.
> 
> I'm not entirely following.  The top-N heapsort approach already
> makes use of the limit info.

Having gone back to look, you're right.  It was Uniq nodes I merged
(the sort handles both bounded-output and dedup).
-- 
Cheers, Jeremy