Re: COUNT(*) very slow on table with primary key
От | Mitch Vincent |
---|---|
Тема | Re: COUNT(*) very slow on table with primary key |
Дата | |
Msg-id | 004c01c12992$0c25c350$1251000a@mitch обсуждение исходный текст |
Ответ на | COUNT(*) very slow on table with primary key (Sheldon Hearn <sheldonh@starjuice.net>) |
Список | pgsql-general |
> Hi folks, > > I've been having trouble with a slow query on a table that has a primary > key (which I understand is supported in PostgreSQL by a UNIQUE non-NULL > index). It's a SELECT COUNT(*) without a WHERE clause; really simple > stuff. If there is no WHERE clause I don't see how anything but a sequential scan could work. I think Tom is working on some more detailed statistics for 7.2 that will help getting the total number of rows in a table quickly, though I can't say for sure.. > The table's pretty wide (about 2.5KB), but has been subjected to a > VACUUM ANALYZE operation in accordance with the advice given in the FAQ. > > Is this just "how it is" or is there more stuff I could look at? I'm > actually trying to speed up a more complex query, but figured it would > be better to report (and get feedback on) the simplest case. If you add a WHERE clause and index the field in the WHERE clause you should get different results. I should say that you should get an index scan if that is what the optomizer thinks in the best plan, if you don't you can force it by setting enable_seqscan to on or off. -Mitch
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