Re: generalizing the planner knobs - Mailing list pgsql-hackers

From Jaime Casanova
Subject Re: generalizing the planner knobs
Date
Msg-id c2d9e70e0512080935m24823f9eke50dff8c2bacb3c@mail.gmail.com
Whole thread Raw
In response to Re: generalizing the planner knobs  ("Jim C. Nasby" <jim@nasby.net>)
Responses Re: generalizing the planner knobs  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
>
> BTW, there's another end to the 'enable_seqscan=false' problem... it
> sometimes doesn't work! Last I looked, enable_seqscan=false only added a
> fixed overhead cost to a seqscan (1000000 IIRC). The problem is, some
> queries will produce estimates for other methodes that are more
> expensive than a seqscan even with the added burden. If instead of
> adding a fixed amount enable_seqscan=false multiplied by some amount
> then this would probably be impossible to occur.
>
> (And before someone asks, no, I don't remember which query was actually
> faster...)
> --
> Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
> Pervasive Software      http://pervasive.com    work: 512-231-6117
> vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461
>

I have often considered that this is an indication that seq scan is
actually the better plan... although, i have to admit that is a little
confusing that  enable_seqscan = false actually let you use a seqscan
if the other plans are bad enough

--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)


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