| From: | "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com> |
|---|---|
| To: | "Lufkin, Brad" <brad(dot)lufkin(at)ngc(dot)com> |
| Cc: | "'psql'" <pgsql-jdbc(at)postgresql(dot)org> |
| Subject: | Re: Query Time |
| Date: | 2003-08-13 20:19:43 |
| Message-ID: | Pine.LNX.4.33.0308131416290.7316-100000@css120.ihs.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-jdbc |
On Wed, 13 Aug 2003, Lufkin, Brad wrote:
> I'm running the following query:
>
> SELECT * FROM someTable LIMIT 20
>
> I turned on explain analyze (tip #8!) and was told that the query plan was
> sequential (no surprise there) with an estimated cost of between 0.00 and
> 1.07. Surprisingly, the actual time was around 90000 msec (or one-and-a-half
> minutes). What's going on?
costs are estimated as a percentage of a cost of a single page access in
sequential mode. I.e. a single sequential page access is assumed to cost
1.0, and everything is relative to that. The cost numbers do NOT
translate directly into any time unit.
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