On Mon, 6 Sep 2004, [iso-8859-15] Pierre-Frédéric Caillaud wrote:

>       Why is it that way ? The planner should use the LIMIT values when  
> planning the query, should it not ?

And it do use limit values, the estimated cost was lower when you had the 

What you need to do is to tune pg for your computer. For example the 
following settings:

 * effective_cache - this setting tells pg how much the os are caching
  (for example use top to find out during a normal work load). You said 
  that the tables fit in memory and by telling pg how much is cached it 
  might adjust it's plans accordingly.

* random_page_cost - how expensive is a random access compared to seq. 
  access. This is dependent on the computer and disk system you have.
  If the setting above does not help, maybe you need to lower this to
  variable to 2 or something.

And don't forget the shared_buffer setting. But most people usually have
it tuned in my experience (but usually too high). Here is an article that
might help you:


/Dennis Björklund

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