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：
sys@ORCL> !sqlplus -v SQL*Plus: Release 10.2.0.1.0 - Production sys@ORCL> !uname -a Linux Think 2.6.18-308.el5xen #1 SMP Fri Jan 27 17:59:00 EST 2012 i686 i686 i386 GNU/Linux
hr@ORCL> conn sh/sh
Connected.
sh@ORCL> select index_name from user_indexes where table_name='CUSTOMERS';
INDEX_NAME
------------------------------
CUSTOMERS_MARITAL_BIX
CUSTOMERS_YOB_BIX
CUSTOMERS_PK
CUSTOMERS_GENDER_BIX
sh@ORCL> drop index CUSTOMERS_MARITAL_BIX;
Index dropped.
sh@ORCL> drop index CUSTOMERS_YOB_BIX;
Index dropped.
sh@ORCL> drop index CUSTOMERS_GENDER_BIX;
Index dropped.
sh@ORCL> drop index CUSTOMERS_PK;
drop index CUSTOMERS_PK
*
ERROR at line 1:
ORA-02429: cannot drop index used for enforcement of unique/primary key
sh@ORCL> create index idx_cust_gender on customers (cust_gender);
Index created.
sh@ORCL> create index idx_cust_postal_code on customers (cust_postal_code);
Index created.
sh@ORCL> create index idx_cust_credit_limit on customers (cust_credit_limit);
Index created.
sh@ORCL> set autot trace
sh@ORCL> ed
Wrote 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: 3555343875
----------------------------------------------------------------------------------------------------
------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|
----------------------------------------------------------------------------------------------------
------
| 0 | SELECT STATEMENT | | 6 | 1080 | 69 (3)| 00:0
0:01 |
| 1 | TABLE ACCESS BY INDEX ROWID | CUSTOMERS | 6 | 1080 | 69 (3)| 00:0
0:01 |
| 2 | BITMAP CONVERSION TO ROWIDS | | | | |
|
| 3 | BITMAP AND | | | | |
|
| 4 | BITMAP CONVERSION FROM ROWIDS| | | | |
|
|* 5 | INDEX RANGE SCAN | IDX_CUST_POSTAL_CODE | 89 | | 1 (0)| 00:0
0:01 |
| 6 | BITMAP CONVERSION FROM ROWIDS| | | | |
|
|* 7 | INDEX RANGE SCAN | IDX_CUST_CREDIT_LIMIT | 89 | | 14 (0)| 00:0
0:01 |
| 8 | BITMAP CONVERSION FROM ROWIDS| | | | |
|
|* 9 | INDEX RANGE SCAN | IDX_CUST_GENDER | 89 | | 52 (2)| 00:0
0:01 |
----------------------------------------------------------------------------------------------------
------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("CUST_POSTAL_CODE"='40804')
7 - access("CUST_CREDIT_LIMIT"=10000)
9 - access("CUST_GENDER"='M')
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
91 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
Cost:205
逻辑读：91
sh@ORCL> set autot off
sh@ORCL> select index_name from user_indexes where table_name='CUSTOMERS';
INDEX_NAME
------------------------------
IDX_CUST_GENDER
IDX_CUST_POSTAL_CODE
IDX_CUST_CREDIT_LIMIT
CUSTOMERS_PK
sh@ORCL> drop index IDX_CUST_GENDER;
Index dropped.
sh@ORCL> drop index IDX_CUST_POSTAL_CODE;
Index dropped.
sh@ORCL> drop index IDX_CUST_CREDIT_LIMIT;
Index dropped.
sh@ORCL> create index idx_cust_gen_pos_cred on customers (cust_gender,cust_postal_code,cust_credit_limit);
Index created.
sh@ORCL> set autot trace
sh@ORCL> ed
Wrote file afiedt.buf
1 select c.*
2 from customers c
3 where cust_gender = 'M' and
4 cust_postal_code = '40840' and
5* cust_credit_limit = 10000
6
sh@ORCL> /
no rows selected
Execution Plan
----------------------------------------------------------
Plan hash value: 3306790926
----------------------------------------------------------------------------------------------------
-
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|
----------------------------------------------------------------------------------------------------
-
| 0 | SELECT STATEMENT | | 6 | 1080 | 8 (0)| 00:00:01
|
| 1 | TABLE ACCESS BY INDEX ROWID| CUSTOMERS | 6 | 1080 | 8 (0)| 00:00:01
|
|* 2 | INDEX RANGE SCAN | IDX_CUST_GEN_POS_CRED | 7 | | 1 (0)| 00:00:01
|
----------------------------------------------------------------------------------------------------
-
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("CUST_GENDER"='M' AND "CUST_POSTAL_CODE"='40840' AND "CUST_CREDIT_LIMIT"=10000)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
1694 bytes sent via SQL*Net to client
374 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
Cost：17
逻辑读：2
sh@ORCL> set autot off
sh@ORCL> select index_name from user_indexes where table_name='CUSTOMERS';
INDEX_NAME
------------------------------
IDX_CUST_GEN_POS_CRED
CUSTOMERS_PK
sh@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> ed
Wrote 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
Cost：8
逻辑读：15