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B-Tree索引性能优于BitMap索引实例

程序员文章站 2022-06-07 13:28:18
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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。 从一致性读

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)

浅析Oracle B-Tree index搜索原理

Oracle索引之B-Tree和Bitmap索引对比

从平衡树到oracle B-Tree索引的原理探索

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 processed

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
----------------------------------------------------------
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)