Re: strange query plan
От | Peter Eisentraut |
---|---|
Тема | Re: strange query plan |
Дата | |
Msg-id | Pine.LNX.4.30.0104081349000.1236-100000@peter.localdomain обсуждение исходный текст |
Ответ на | strange query plan (Mario Weilguni <mweilguni@sime.com>) |
Список | pgsql-general |
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/
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