| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
| Cc: | "Matthew Wakeling" <matthew(at)flymine(dot)org>, "Craig Ringer" <craig(at)postnewspapers(dot)com(dot)au>, jmpoure(at)free(dot)fr, "PostgreSQL Performance" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Order by (for 15 rows) adds 30 seconds to query time |
| Date: | 2009-12-02 20:25:26 |
| Message-ID: | 21616.1259785526@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Craig Ringer <craig(at)postnewspapers(dot)com(dot)au> wrote:
>> Doesn't the planner have some ... issues ... with estimation of
>> row counts on joins over unions? Or is my memory just more faulty
>> than usual?
> So far I can't tell if it's views with unions or (as I suspect)
> inheritance.
As of recent versions there shouldn't be a lot of difference between
inheritance and UNION ALL subqueries --- they're both "appendrels"
to the planner. And yeah, I think the statistical support is pretty
crummy.
regards, tom lane
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