Well i guess that there are cases where that is not so.However i 
understand that postgres does not have any way accept
the automatic.
Tom Lane wrote:
>Tsirkin Evgeny <tsurkin(at)mail(dot)jct(dot)ac(dot)il> writes:
>  
>
>>What i realy want is to say to postgres that the particular
>>table should be cached .
>>    
>>
>
>Adopting the position that you are smarter than an automatic
>optimization algorithm is generally a good way to achieve less
>performance, not more.  
>