Re: The use of cpu_index_tuple_cost by the query planner

Thanks,

I had to look in the soure code for the other parameters as well. I was
trying to create some queries because I was interested in the relation
between estimated cost and actual time.

Regards,

Antonio Carlos Furtado

On Wed, Jun 27, 2012 at 8:22 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:

> On Wed, 2012-06-27 at 21:37 +0100, Simon Riggs wrote:
> > On 27 June 2012 21:28, Antonio Carlos Salzvedel Furtado Junior
> > <acsfj08(at)inf(dot)ufpr(dot)br> wrote:
> >
> > > I'm trying to understand the use of PostgreSQL tuning parameters by the
> > > query planner's cost estimator. I'm trying to use simple queries to
> > > understand how these parameters would affect the estimated cost.
> However, I
> > > haven't still been able to see the cpu_index_tuple_cost.
> >
> > Your best hope is to read the source code. Things will become much
> clearer.
>
> Right, the cost model is too complex to really understand just running
> EXPLAIN.
>
> The tuning parameters are translated to global variables
> in ./src/backend/utils/misc/guc.c. From there, you can search for
> references to the global variables (often with very similar names to the
> tuning parameter) and find out how they are used in the cost model.
>
> Regards,
> Jeff Davis
>
>