Re: Slow count(*) again...

  On 10/13/2010 3:19 AM, Mark Kirkwood wrote:
> I think that major effect you are seeing here is that the UPDATE has
> made the table twice as big on disk (even after VACUUM etc), and it has
> gone from fitting in ram to not fitting in ram - so cannot be
> effectively cached anymore.
>
In the real world, tables are larger than the available memory. I have 
tables of several hundred gigabytes in size. Tables shouldn't be 
"effectively cached", the next step would be to measure "buffer cache 
hit ratio", tables should be effectively used.

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Mladen Gogala
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