Re: Yet again on indices...

On Wed, 2002-02-27 at 14:48, Jean-Paul ARGUDO wrote:

Ok,

I'm working on query analysis for a program in ecpg for business puposes. Look
at what I found on with PG 7.2: Please be cool with my french2english processor,
I got few bogomips in my brain dedicated to english (should have listen more in
class..):
----

line 962 (in the ecpg source..)

EXPLAIN SELECT t12_bskid, t12_pnb, t12_lne, t12_tck
FROM T12_20011231
WHERE t12_bskid >= 1
ORDER BY t12_bskid, t12_pnb, t12_tck, t12_lne;

...

=> Uh? Seq scan cheaper than index???

=> let's disable seqscan to read cost of index:
postgresql.conf : enable_seqscan = false

You could just do

set enable_seqscan to 'off'

in sql

Sort (cost=3126.79..3126.79 rows=25693 width=46)
-> Index Scan using t12_idx_bskid_20011231 on t12_20011231
(cost=0.00..1244.86 rows=25693 width=46)

=> Uh? seq scan'cost is lower than index scan?? => mailto hackers

It often is. Really.

----

What's your opinion?

What are the real performance numbers ?

If they are other than what postgresql optimiser thinks you can change
them in system table.

----------------
Hannu