I bet that if you changed SMC_MAP_CURRSTAT_NUK : --> (MAP_ID, CURR_STATUS_ID, MAP_VERSION) to SMC_MAP_CURRSTAT_NUK :--> ( MAP_VERSION,CURR_STATUS_ID, MAP_ID) it would be a *better* index.For the first query, Oracle isn't exactly doing the same sort of operation on the two Indexes.
The AllEqRange on SMC_MAP_CURRSTAT_NUK has a much higher I/O cost than then RangeScan on SMC_IDX4 and that is why Oracle chooses the latter index. The expected cardinality is derived from *column* statistics. Hemant K Chitale At 09:22 PM Wednesday, Denis wrote:
Hi, Listers, I had a problem and appreicate you help me to understand:Problem : suboptimal execution plan using index SMC_IDX4 selected by Oracle CBOgood index: SMC_MAP_CURRSTAT_NUK(MAP_ID, CURR_STATUS_ID, MAP_VERSION) bad index : SMC_IDX4(MAP_ID, PREV_STATUS_ID, CURR_STATUS_ID )Question (refer to 10053 below) : how ix_sel = 0.0017921 is calculated for the index (SMC_MAP_CURRSTAT_NUK) access path ?My understanding is selectivity(MAP_ID,MAP_VERSION,CURR_STATUS_ID)= selectivity(MAP_ID) * selectivity(MAP_VERSION) * selectivity(CURR_STATUS_ID)= 0.012821 * 1 * 0.023256 = 2.9817e-04 Oracle version: 10.2.0.4 SQL-1: SELECT pieid FROM SMC WHERE MAP_ID = 91 AND MAP_VERSION = 1 AND CURR_STATUS_ID = 10; ===> from 10053 trace Table Stats:: Table: SMC Alias: SMC #Rows: 299321835 #Blks: 9470379 AvgRowLen: 186.00 ----------------------------------------- BEGIN Single Table Cardinality Estimation ----------------------------------------- Column (#8): MAP_ID(NUMBER) AvgLen: 4.00 NDV: 78 Nulls: 0 Density: 0.012821 Min: 1 Max: 144 Column (#9): MAP_VERSION(NUMBER) AvgLen: 3.00 NDV: 1 Nulls: 0 Density: 1 Min: 1 Max: 1 Column (#7): CURR_STATUS_ID(NUMBER) AvgLen: 3.00 NDV: 43 Nulls: 0 Density: 0.023256 Min: 0 Max: 97 Table: SMC Alias: SMCCard: Original: 299321835 Rounded: 89243 Computed: 89243.24 Non Adjusted: 89243.24Index: SMC_MAP_CURRSTAT_NUK Col#: 8 7 9LVLS: 3 #LB: 752377 #DK: 558 LB/K: 1348.00 DB/K: 204576.00 CLUF: 114153723.00Index: SMC_IDX4 Col#: 8 6 7LVLS: 3 #LB: 756804 #DK: 2060 LB/K: 367.00 DB/K: 60536.00 CLUF: 124705545.00Access Path: index (AllEqRange) Index: SMC_MAP_CURRSTAT_NUK resc_io: 205929.00 resc_cpu: 1743632975 ix_sel: 0.0017921 ix_sel_with_filters: 0.0017921 Cost: 206118.49 Resp: 206118.49 Degree: 1 Access Path: index (RangeScan) Index: SMC_IDX4 resc_io: 46888.00 resc_cpu: 1159030959 ix_sel: 0.012821 ix_sel_with_filters: 2.9815e-04 Cost: 47034.81 Resp: 47034.81 Degree: 1 SQL-2: SELECT pieid FROM SMC WHERE MAP_ID = 91 AND CURR_STATUS_ID = 10;In this case, CBO is able to choose better index access path and selectivity calculation is understandable.Access Path: index (RangeScan) Index: SMC_MAP_CURRSTAT_NUK resc_io: 34264.00 resc_cpu: 288336758 ix_sel: 2.9815e-04 ix_sel_with_filters: 2.9815e-04 Cost: 34295.33 Resp: 34295.33 Degree: 1 Access Path: index (RangeScan) Index: SMC_IDX4 resc_io: 46888.00 resc_cpu: 1152783475 ix_sel: 0.012821 ix_sel_with_filters: 2.9815e-04 Cost: 47034.13 Resp: 47034.13 Degree: 1 Thanks, Yu (Denis) Sun Oracle DBA
Hemant K Chitale http://hemantoracledba.blogspot.com http://hemantscribbles.blogspot.com http://web.singnet.com.sg/~hkchital -- //www.freelists.org/webpage/oracle-l