| From: | Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> |
|---|---|
| To: | pgsql-hackers(at)postgresql(dot)org |
| Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, josh(at)agliodbs(dot)com, "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: [HACKERS] Hints proposal |
| Date: | 2006-10-18 02:18:52 |
| Message-ID: | 200610172218.53194.xzilla@users.sourceforge.net |
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| Lists: | pgsql-hackers pgsql-performance |
On Friday 13 October 2006 12:46, Gregory Stark wrote:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
> >> > I actually think the way to attack this issue is to discuss the kinds
> >> > of errors the planner makes, and what tweaks we could do to correct
> >> > them. Here's the ones I'm aware of:
> >> >
> >> > -- Incorrect selectivity of WHERE clause
> >> > -- Incorrect selectivity of JOIN
> >> > -- Wrong estimate of rows returned from SRF
> >> > -- Incorrect cost estimate for index use
> >> >
> >> > Can you think of any others?
>
> -- Incorrect estimate for result of DISTINCT or GROUP BY.
Yeah, that one is bad. I also ran into one the other day where the planner
did not seem to understand the distinctness of a columns values across table
partitions...
--
Robert Treat
Build A Brighter LAMP :: Linux Apache {middleware} PostgreSQL
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