Обсуждение: abou the cost estimation
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 ______________________________________ =================================================================== �������ѵ������� (http://mail.sina.com.cn) ���˷�����Ϣ�������г���һ�ߣ��ó���ʱ�ͳ��֣� (http://classad.sina.com.cn/2shou/) �������ֻ�ͼƬ������������������ѡ��ÿ�춼�и��� (http://sms.sina.com.cn/cgi-bin/sms/smspic.cgi)
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