Please supply the tkprof output you are using to get these figures. Is your "cost about 30k" from the Rowsource Operation output, showing "time = 30000 microseconds" ? Or is it actually from a plan_table. If the latter, then a CPU cost of around 30,000 (Oracle operations) is perfectly reasonable for 4 buffer visits to acquire a single row by unique index. Regards Jonathan Lewis http://jonathanlewis.wordpress.com Author: Cost Based Oracle: Fundamentals http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html----- Original Message -----
Subject: RE: prefixed index - high clustering factor & high cpu
at the tkprof the cpu cost is very high , its about 30k, rows returned is 1 , io cost is 4 , the cost itself only 4.