B-Tree索引性能优于BitMap索引实例

一、实验说明： 操作系统：rhel 5.4 x86 数据库：Oracle 11g R2 实验说明：该实验是为了说明B-Tree索引性能优于BitMap索引的情况。 Oracle B树索引简介（B-Tree Index） http://www.linuxidc.com/Linux/2013-03/80754.htm浅析Oracle B-Tree index搜索原理 http://www.linuxidc.com/Linux/2012-08/68578.htmOracle索引之B-Tree和Bitmap索引对比 http://www.linuxidc.com/Linux/2012-03/57460.htm从平衡树到oracle B-Tree索引的原理探索 http://www.linuxidc.com/Linux/2012-08/67524.htm二、实验操作：首先创建一张t_btree表，并建立B-Tree索引，索引键是object_id：SQL> create table t_btree as select * from dba_objects;Table created.SQL> create index ind_tree on t_btree（object_id）;Index created.执行两次下面的查询语句，并显示执行计划：SQL> set autotrace traceonly;
SQL> select * from t_btree where object_id=9899;
Execution Plan
----------------------------------------------------------
Plan hash value: 447474086----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 2 （0）| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T_BTREE | 1 | 207 | 2 （0）| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IND_TREE | 1 | | 1 （0）| 00:00:01 |
----------------------------------------------------------------------------------------Predicate Information （identified by operation id）:
--------------------------------------------------- 2 - access（"OBJECT_ID"=9899）Note
-----
- dynamic sampling used for this statement （level=2）
Statistics
----------------------------------------------------------
312 recursive calls
0 db block gets
108 consistent gets
289 physical reads
0 redo size
1404 bytes sent via SQL*Net to client
419 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts （memory）
0 sorts （disk）
1 rows processedSQL> select * from t_btree where object_id=9899;
Execution Plan
----------------------------------------------------------
Plan hash value: 447474086----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 2 （0）| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T_BTREE | 1 | 207 | 2 （0）| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IND_TREE | 1 | | 1 （0）| 00:00:01 |
----------------------------------------------------------------------------------------Predicate Information （identified by operation id）:
--------------------------------------------------- 2 - access（"OBJECT_ID"=9899）Note
-----
- dynamic sampling used for this statement （level=2）
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
1404 bytes sent via SQL*Net to client
419 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts （memory）
0 sorts （disk）
1 rows processed同样执行之前的语句两次：SQL> select * from t_bmap where object_id=9899;
Execution Plan
----------------------------------------------------------
Plan hash value: 3763176822----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 110 （0）| 00:00:02 |
| 1 | TABLE ACCESS BY INDEX ROWID | T_BMAP | 1 | 207 | 110 （0）| 00:00:02 |
| 2 | BITMAP CONVERSION TO ROWIDS| | | | | |
|* 3 | BITMAP INDEX SINGLE VALUE | IND_MAP | | | | |
----------------------------------------------------------------------------------------Predicate Information （identified by operation id）:
--------------------------------------------------- 3 - access（"OBJECT_ID"=9899）Note
-----
- dynamic sampling used for this statement （level=2）
Statistics
----------------------------------------------------------
312 recursive calls
0 db block gets
98 consistent gets
266 physical reads
0 redo size
1404 bytes sent via SQL*Net to client
419 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts （memory）
0 sorts （disk）
1 rows processedSQL> select * from t_bmap where object_id=9899;
Execution Plan
----------------------------------------------------------
Plan hash value: 3763176822----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 110 （0）| 00:00:02 |
| 1 | TABLE ACCESS BY INDEX ROWID | T_BMAP | 1 | 207 | 110 （0）| 00:00:02 |
| 2 | BITMAP CONVERSION TO ROWIDS| | | | | |
|* 3 | BITMAP INDEX SINGLE VALUE | IND_MAP | | | | |
----------------------------------------------------------------------------------------Predicate Information （identified by operation id）:
--------------------------------------------------- 3 - access（"OBJECT_ID"=9899）Note
-----
- dynamic sampling used for this statement （level=2）
Statistics
----------------------------------------------------------
7 recursive calls
0 db block gets
68 consistent gets
0 physical reads
0 redo size
1404 bytes sent via SQL*Net to client
419 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts （memory）
0 sorts （disk）
1 rows processed从上面的查询中，我们可以得到，分别给两张内容一样的表做查询的时候，在执行第二次的时候是属于软解析：从一致性读上比较，B-Tree索引的consistent gets是4，BitMap的是68；从Cost的消耗上看，B-Tree索引的COST是2，而BitMap的是110。在索引键是主键或者唯一性约束的情况下B-Tree索引的效率要优于BitMap索引。更多Oracle相关信息见Oracle 专题页面 http://www.linuxidc.com/topicnews.aspx？tid=12本文永久更新链接地址