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