| From: | Richard Huxton <dev(at)archonet(dot)com> |
|---|---|
| To: | "A(dot) Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com> |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: many 'OR' in WHERE-condition |
| Date: | 2007-04-20 11:59:01 |
| Message-ID: | 4628AB05.6000400@archonet.com |
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| Lists: | pgsql-sql |
A. Kretschmer wrote:
>
> It's not my problem - i found it in a forum (german)
> http://pg-forum.de/showthread.php?t=1332
>
> If the list contains up to 195 entrys -> up to 195 bitmap index scans
> and BitmapOr -> 7.839ms
>
> If the list contains 196 entrys -> seq-scan -> 5591.567ms
It looks like it's getting the row estimate badly wrong.
"Seq Scan on t_datasets_searchindices_rel (cost=0.00..129053.50
rows=159277 width=4) (actual time=0.213..5590.435 rows=325 loops=1)
Probably worth increasing the statistics estimate for that column (ALTER
TABLE ... ALTER COLUMN ... SET STATISTICS=N)
It also looks like it's getting the cost estimates badly wrong. Probably
worth asking the original poster to read the tuning guide.
--
Richard Huxton
Archonet Ltd
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