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Re: Various performance questions

From: Dror Matalon <dror(at)zapatec(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Various performance questions
Date: 2003-10-27 07:43:57
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Lists: pgsql-performance
On Mon, Oct 27, 2003 at 12:52:27PM +0530, Shridhar Daithankar wrote:
> Dror Matalon wrote:
> >On Mon, Oct 27, 2003 at 01:04:49AM -0500, Christopher Browne wrote:
> >>Most of the time involves:
> >>
> >>a) Reading each page of the table, and
> >>b) Figuring out which records on those pages are still "live."
> >
> >
> >The table has been VACUUM ANALYZED so that there are no "dead" records.
> >It's still not clear why select count() would be slower than select with
> >a "where" clause.
> Do a vacuum verbose full and then everything should be within small range 
> of each other.

I did vaccum full verbose and the results are the same as before, 55
seconds for count(*) and 26 seconds for count(*) where channel < 5000.

> Also in the where clause, does explicitly typecasting helps?
> Like 'where channel<5000::int2;'

It makes no difference.

>  HTH
>  Shridhar

Dror Matalon
Zapatec Inc 
1700 MLK Way
Berkeley, CA 94709

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