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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�Senior Engineer Web Solutions Nikolaiplatz 4
�tel: +43-316-813824 � � � � 8020 graz, austria
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Mario Weilguni writes:
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.
Since your query reads the entire "log" table, it is certainly better to
use a sequential scan in the case of sum() and avg(). A min() and max()
would theoretically not need to scan the entire table in the presence of
an index, but unfortunately this doesn't work yet.
--
Peter Eisentraut peter_e@gmx.net http://yi.org/peter-e/
Hi Peter,
I've been testing the compilation process of 7.1RC3 with the newest
release of OpenSSL (0.9.6a) today. The des_encrypt() namespace conflict
is no longer present on Solaris 8 (SPARC nor INTEL). So it looks like
the OpenSSL guys have renamed the conflicting functions.
Is this something worth mentioning in the Solaris-FAQ (and probably the
Unixware-FAQ)?
Regards and best wishes,
Justin Clift
Justin Clift writes:
I've been testing the compilation process of 7.1RC3 with the newest
release of OpenSSL (0.9.6a) today. The des_encrypt() namespace conflict
is no longer present on Solaris 8 (SPARC nor INTEL). So it looks like
the OpenSSL guys have renamed the conflicting functions.Is this something worth mentioning in the Solaris-FAQ (and probably the
Unixware-FAQ)?
Indeed. Thanks.
--
Peter Eisentraut peter_e@gmx.net http://yi.org/peter-e/