Re: wrong query plan in 7.1beta3

On Sat, 27 Jan 2001, Peter Eisentraut wrote:

> Kovacs Zoltan writes:
>
> > There seems to be an optimizer problem in 7.1beta3. The query you can see
> > below worked fast in 7.0.2 but in 7.1beta3 is rather slow. The problem is
> > that an 'index scan' has been changed to a 'seq scan'. Details:
>
> > Subquery Scan sd_user_grant (cost=38.68..38.85 rows=1 width=61)
> > -> Aggregate (cost=38.68..38.85 rows=1 width=61)
> > -> Group (cost=38.68..38.73 rows=10 width=61)
> > -> Sort (cost=38.68..38.68 rows=10 width=61)
> > -> Nested Loop (cost=0.00..38.51 rows=10 width=61)
> > -> Seq Scan on pg_shadow (cost=0.00..1.01 rows=1 width=32)
> > -> Seq Scan on sd_grant (cost=0.00..20.00 rows=1000 width=29)
>
> You haven't VACUUM ANALYZE'd the sd_grant table. Therefore the row
> estimate is way off (1000 vs 6) and thus a sequential scan is (correctly)
> thought to be faster.
>
>

Thanks, I tried it.

tir=# explain select sel,ins,upd,del,rul from sd_user_grant where
tabla='cikk' and usename::varchar='1016';
NOTICE: QUERY PLAN:

Subquery Scan sd_user_grant (cost=8.00..8.03 rows=1 width=61)
-> Aggregate (cost=8.00..8.03 rows=1 width=61)
-> Group (cost=8.00..8.01 rows=2 width=61)
-> Sort (cost=8.00..8.00 rows=2 width=61)
-> Nested Loop (cost=0.00..7.99 rows=2 width=61)
-> Seq Scan on pg_shadow (cost=0.00..1.01
rows=1 width=32)
-> Seq Scan on sd_grant (cost=0.00..3.81
rows=181 width=29)

It seems to be a little bit faster, but it's still very-very slow.
The 'seq scan' on sd_grant still remained.

Zoltan
--
Kov\'acs, Zolt\'an
kovacsz(at)pc10(dot)radnoti-szeged(dot)sulinet(dot)hu
http://www.math.u-szeged.hu/~kovzol
ftp://pc10.radnoti-szeged.sulinet.hu/home/kovacsz