strange query plan

I've a table containing some sort of logs, the table layout ist:
Attribute | Type | Modifier
-----------+--------------------------+---------------------------------------
id | integer | not null default nextval('ids'::text)
serverid | integer | not null
ts | timestamp with time zone | default now()
log | character varying(400) | not null
Indices: i1,
log_pkey

primary key is id, and there is an additional index on serverid. The table
contains ~ 1.4 mio of rows, I've used "vacuum analyze".

Now when I type:
explain select min(id)from log;
NOTICE: QUERY PLAN:

Aggregate (cost=45702.20..45702.20 rows=1 width=4)
-> Seq Scan on log (cost=0.00..41978.36 rows=1489536 width=4)

I don't understand why the index log_pkey is not used here. I guess it would
be much cheaper to consult the index to get min(), max(), sum() and avg()
instead of sequentially scanning ~500MB of data.

Any idea?

Thanks

Best regards,
Mario Weilguni

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Mario Weilguni                 KPNQwest Austria GmbH
 Senior Engineer Web Solutions Nikolaiplatz 4
 tel: +43-316-813824         8020 graz, austria
 fax: +43-316-813824-26       http://www.kpnqwest.at
 e-mail: mario(dot)weilguni(at)kpnqwest(dot)com
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