There's a quite nice description in the docs:
http://www.postgresql.org/docs/9.0/interactive/row-estimation-examples.html
and a some more details for indexes:
http://www.postgresql.org/docs/9.0/interactive/index-cost-estimation.html
A bit more info about how this is used is available in this presentation:
http://momjian.us/main/writings/pgsql/internalpics.pdf
But if you need more details, then I quess the best approach to get it
is to read the sources (search for the cost estimation etc.).
regards
Tomas
Dne 10.4.2011 20:22, Radhya sahal napsal(a):
> Dear ,all
> i would to ask you about how postgresql optimizer parameters :-
> 1- random page cost
>
> 2- cpu tuple cost
>
> 3- cpu operator cost
>
> 4- cpu index tuple cost
>
> 5- effective cache size
>
> play as parameters in cost estimator equation
>
> i imagine that cost function is the same as
>
> f(x,y,z,....)=ax+by......
>
> cost(cpu tuple cost,cpu operator cost,....)
>
> can any one help me to know the equation that cost estimator used it..
>
> My regard
>
> Radhya,,,,
>
>
>
