Re: Number of disk pages obtained by explain analyze

On Tue, 24 Sep 2002, Tourtounis Sotiris wrote:

> I have a table of the form || att0 int4 | att1 int4 | att2 int4 ||
> and i declare an index on att0.
>
> With the SQL query
> "select * from pg_class where relnane = 'Name of Table'
>
> i get the information of created disk pages = 1623. However when i run an
> sql query of the form "select att0 from table where att0 < A(int4) and
> att0> B(int4)" i get through explain analyze the following result, which
> as we see refers that in actual time have as total cost 4362.73 disk
> pages. Are they the same thing or those two refer to different referring
> characteristics?Thank you!!

The cost is an estimate of work, not precisely disk pages (for example
random page reads default to 4 units iirc, sequential reads default to 1
unit, there's some cost for cpu work) You can find the values in
postgresql.conf.