Hello, All
    I have read the source code  /cvsroot/pgsql/src/backend/optimizer/path/costsize.c and there is a function cost_sort(...). I think the code in 464 to 465 lines must be changed to:
     startup_cost += npageaccesses *
	   (1.0 + cost_nonsequential_access(1)) * 0.5;

The original code is:
     startup_cost += npageaccesses *
	    (1.0 + cost_nonsequential_access(npages)) * 0.5;
Can any one discuss about this issue with me ? Thanks for your response very much!
----------------------
 Guo long jiang. 2002-9-6 
 
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Fri, 06 Sep 2002 16:09:59 +0800
ljguo_1234 <ljguo_1234@sina.com>
abou the cost estimation
ljguo_1234 <ljguo_1234@sina.com> writes:
>     I have read the source code  /cvsroot/pgsql/src/backend/optimizer/path/costsize.c and there is a function cost_sort(...). I think the code in 464 to 465 lines must be changed to:
>      startup_cost += npageaccesses *
> 	   (1.0 + cost_nonsequential_access(1)) * 0.5;

That would be wrong.  Note the definition of cost_nonsequential_access:

 *	  Estimate the cost of accessing one page at random from a relation
 *	  (or sort temp file) of the given size in pages.

			regards, tom lane

Fri, 06 Sep 2002 09:01:05 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: abou the cost estimation 