深入理解Oracle索引（7）：用实验数据观察从B-tree索引→复合索引→Bitmap索引所消费的CPU和I/O

环境：

sh@ORCL> set autot offsh@ORCL> select index_name from user_indexes where table_name='CUSTOMERS';INDEX_NAME------------------------------IDX_CUST_GEN_POS_CREDCUSTOMERS_PKsh@ORCL> drop index IDX_CUST_GEN_POS_CRED;Index dropped.sh@ORCL> create bitmap index idx_cust_gender on customers(cust_gender);Index created.sh@ORCL> create bitmap index idx_cust_postal_code on customers (cust_postal_code);Index created.sh@ORCL> create bitmap index idx_cust_credit_limit on customers(cust_credit_limit);Index created.sh@ORCL> edWrote file afiedt.buf  1  select c.*  2    from customers c  3   where cust_gender = 'M' and  4         cust_postal_code = '40804' and  5*        cust_credit_limit = 10000  6  sh@ORCL> /6 rows selected.Execution Plan----------------------Plan hash value: 724066067------------------------------------------------------------------| Id  | Operation                    | Name                  | Rows  | Bytes | Cost (%CPU)| Time |------------------------------------------------------------------|   0 | SELECT STATEMENT             |                       |     6 |  1080 |     4   (0)| 00:00:01 ||   1 |  TABLE ACCESS BY INDEX ROWID | CUSTOMERS             |     6 |  1080 |     4   (0)| 00:00:01 ||   2 |   BITMAP CONVERSION TO ROWIDS|                       |       |       |            | ||   3 |    BITMAP AND                |                       |       |       |            | ||*  4 |     BITMAP INDEX SINGLE VALUE| IDX_CUST_POSTAL_CODE  |       |       |            | ||*  5 |     BITMAP INDEX SINGLE VALUE| IDX_CUST_CREDIT_LIMIT |       |       |            | ||*  6 |     BITMAP INDEX SINGLE VALUE| IDX_CUST_GENDER       |       |       |            | |------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------   4 - access("CUST_POSTAL_CODE"='40804')   5 - access("CUST_CREDIT_LIMIT"=10000)   6 - access("CUST_GENDER"='M')Statistics----------------------          0  recursive calls          0  db block gets         15  consistent gets          0  physical reads          0  redo size       2974  bytes sent via SQL*Net to client        385  bytes received via SQL*Net from client          2  SQL*Net roundtrips to/from client          0  sorts (memory)          0  sorts (disk)          6  rows processed