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Home -> Community -> Mailing Lists -> Oracle-L -> 54 is less than 4 for CBO ? solved
Thanks for the explanation Jonathan,
the digits are fitting pretty well to your your explanation of points 1) and 2) :
I have
First K Rows: K/N ratio = 0,000001091131285
Join cardinality (N) is 916480 =>
1/N = 1/ 916480 = 0,000001091131285 = K/N ratio!
CBO is (supposedly) adjusting the cardinality of the join to the optmizer goal (FIRST_ROWS(1),FIRST_ROWS(10) etc ) using the adjusted join cardinality factor (First K Rows: K/N ratio line in the 10053 trace file).
The samples (format is HINT => join card of 10053 event trace file):
base, no hints = > Join cardinality: 916480 = outer (303367558) * inner (31768) *
sel (9.5096e-08)
FIRST_ROWS(1) => Join cardinality: 1 = outer (332) * inner (31768) *
sel (9.5096e-08)
FIRST_ROWS(10) => Join cardinality: 10 = outer (3311) * inner (31768) *
sel (9.5096e-08)
FIRST_ROWS(100) => Join cardinality: 100 = outer (33102) * inner (31768) *
sel (9.5096e-08) FIRST_ROWS(1000) => Join cardinality: 1000 = outer (331014) * inner (31768) * sel (9.5096e-08)
Best Regards. Milen
Roughly speaking:
Regards
Jonathan Lewis http://www.oracle.com/technology/community/oracle_ace/ace1.html#lewis
The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html
Cost Based Oracle: Fundamentals http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html
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