SQL> select * from v$version where rownum<2;
BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
SQL> create table t as select * from dba_objects; Table created. SQL> create index idx_t on t(object_id); Index created. SQL> BEGIN 2 DBMS_STATS.GATHER_TABLE_STATS(ownname => 'TEST', 3 tabname => 'T', 4 estimate_percent => 100, 5 method_opt => 'for all columns size auto', 6 degree => DBMS_STATS.AUTO_DEGREE, 7 cascade => TRUE); 8 END; 9 / PL/SQL procedure successfully completed. SQL> select leaf_blocks,blevel,clustering_factor from dba_indexes where index_name='IDX_T'; LEAF_BLOCKS BLEVEL CLUSTERING_FACTOR ----------- ---------- ----------------- 161 1 1636 SQL> select a.column_name, 2 b.num_rows, 3 a.num_distinct, 4 a.num_nulls, 5 utl_raw.cast_to_number(high_value) high_value, 6 utl_raw.cast_to_number(low_value) low_value, 7 (b.num_rows-a.num_nulls) "NUM_ROWS-NUM_NULLS", 8 utl_raw.cast_to_number(high_value)- utl_raw.cast_to_number(low_value)"HIGH_VALUE-LOW_VALUE", 9 density, 10 a.histogram, 11 a.num_buckets 12 from dba_tab_col_statistics a, dba_tables b 13 where a.owner = b.owner 14 and a.table_name = b.table_name 15 and a.owner ='TEST' 16 and a.table_name = upper('T') 17 and a.column_name='OBJECT_ID'; COLUMN_NAME NUM_ROWS NUM_DISTINCT NUM_NULLS HIGH_VALUE LOW_VALUE NUM_ROWS-NUM_NULLS HIGH_VALUE-LOW_VALUE DENSITY HISTOGRAM NUM_BUCKETS -------------------- ---------- ------------ ---------- ---------- ---------- ------------------ -------------------- ---------- --------------- ----------- OBJECT_ID 72469 72469 0 74664 2 72469 74662 .000013799 NONE 1 SQL> alter session set optimizer_features_enable='9.2.0'; Session altered. SQL> select owner from t where object_id<1000; 942 rows selected. Elapsed: 00:00:00.07 Execution Plan ---------------------------------------------------------- Plan hash value: 1594971208 --------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost | --------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 969 | 10659 | 26 | | 1 | TABLE ACCESS BY INDEX ROWID| T | 969 | 10659 | 26 | |* 2 | INDEX RANGE SCAN | IDX_T | 969 | | 4 | --------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("OBJECT_ID"<1000) Note ----- - cpu costing is off (consider enabling it) cost = blevel + celiling(leaf_blocks *effective index selectivity) + celiling(clustering_factor * effective table selectivity) SQL> select 1+ceil(161*(1000-2)/74662)+ceil(1636*(1000-2)/74662) from dual; 1+CEIL(161*(1000-2)/74662)+CEIL(1636*(1000-2)/74662) ---------------------------------------------------- 26 SQL> alter session set optimizer_features_enable='11.2.0.1'; Session altered. SQL> select owner from t where object_id<1000; 942 rows selected. Elapsed: 00:00:00.05 Execution Plan ---------------------------------------------------------- Plan hash value: 1594971208 ------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 969 | 10659 | 26 (0)| 00:00:01 | | 1 | TABLE ACCESS BY INDEX ROWID| T | 969 | 10659 | 26 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | IDX_T | 969 | | 4 (0)| 00:00:01 | ------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("OBJECT_ID"<1000)