| From: | "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Bruce Momjian" <bruce(at)momjian(dot)us> |
| Cc: | "Marten Verhoeven" <m(dot)verhoeven(at)van-beek(dot)nl>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Slow performance with left outer join |
| Date: | 2008-01-21 18:04:33 |
| Message-ID: | 162867790801211004q3b01f0a3hb97d162392ac037@mail.gmail.com |
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| Lists: | pgsql-performance |
Hello
> > Filter: ((COALESCE((at_type)::integer, 1) = 1) AND (COALESCE(at_language, 0::numeric) = 0::numeric))
>
> If this is slow, it must be that the scan of fpuarticletext actually
> returns many more rows than the single row the planner is expecting.
> The reason the estimate is off is probably that the planner cannot make
> any useful estimate about those COALESCE expressions. Try rewriting
> them in the simpler forms
>
> (at_type = 1 or at_type is null) AND
> (at_language = 0 or at_language is null)
>
what about put this topic into FAQ.
Regards
Pavel Stehule
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