| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Chris Kratz <chris(dot)kratz(at)vistashare(dot)com> |
| Cc: | Decibel! <decibel(at)decibel(dot)org>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Incorrect estimates on correlated filters |
| Date: | 2008-08-13 20:58:30 |
| Message-ID: | 20080813205830.GC4672@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-performance |
Chris Kratz wrote:
> Unfortunately, if I don't think the sorting idea would help in the one case
> I'm looking at which involves filters on two tables that are joined
> together. The filters happen to be correlated such that about 95% of the
> rows from each filtered table are actually returned after the join.
> Unfortunately, the planner thinks we will get 1 row back.
Maybe you can wrap that part of the query in a SQL function and set its
estimated cost to the real values with ALTER FUNCTION ... ROWS.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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