Bug or feature?

pgSQL 7.2.1, table with ~590000 rows with next stuct:

user_id       integer
url           text
.................... -- other fields

i do VACUUM ANALYZE, and then have this results:


1) ----------
proxy=> EXPLAIN SELECT count(user_id) AS cnt, user_id FROM stats GROUP 
BY user_id ORDER BY cnt DESC;
NOTICE:  QUERY PLAN:

Sort  (cost=94399.52..94399.52 rows=58842 width=4)
   ->  Aggregate  (cost=86383.49..89325.61 rows=58842 width=4)
         ->  Group  (cost=86383.49..87854.55 rows=588425 width=4)
               ->  Sort  (cost=86383.49..86383.49 rows=588425 width=4)
                     ->  Seq Scan on stats  (cost=0.00..13873.25 
rows=588425 width=4)


2) ----------
proxy=> EXPLAIN SELECT count(url) AS cnt, user_id FROM stats GROUP BY 
user_id ORDER BY cnt DESC;
NOTICE:  QUERY PLAN:

Sort  (cost=155022.05..155022.05 rows=58842 width=51)
   ->  Aggregate  (cost=146163.49..149105.61 rows=58842 width=51)
         ->  Group  (cost=146163.49..147634.55 rows=588425 width=51)
               ->  Sort  (cost=146163.49..146163.49 rows=588425 width=51)
                     ->  Seq Scan on stats  (cost=0.00..13873.25 
rows=588425 width=51)

-----------end-----------

cost grow by 1.5 times!
yes, i understand - this because url column have big width...
but in count(url) width of column not important! - but used?...
or it's bug of optimizer? or it's not implemented in optimizer?

Thx.

ps : sorry for my bad english :)

-- 
With best wishes, DIGMA sysadmin
Oleg Kostyuk aka Cub (CUB7-RIPE)
[BSD registered user #BSD050664]