| From: | Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org> |
|---|---|
| To: | Richard van den Berg <richard(dot)vandenberg(at)trust-factory(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Explain not accurate |
| Date: | 2004-01-11 19:55:00 |
| Message-ID: | Pine.LNX.4.44.0401112050470.13405-100000@zigo.dhs.org |
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| Thread: | |
| Lists: | pgsql-performance |
On Fri, 9 Jan 2004, Richard van den Berg wrote:
> problems. However, I've run into an issue where explain tells us a the
> costs of a quiry are tremendous (105849017586), but the query actually
> runs quite fast. Even "explain analyze" shows these costs.
It would be helpful if you can show the query and the EXPLAIN ANALYZE of
the query (and not just EXPLAIN).
> This makes me wonder: can the estimates explain shows be dead wrong?
Of course they can. An estimation is just an estimation. If you have not
analyzed the database then it's most likely wrong. Dead wrong is not
common, but not impossible.
Run VACUUM ANALYZE and see if the estimate is better after that.
--
/Dennis Björklund
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