在《SQL Tuning 基础概述05 - Oracle 索引类型及介绍》的1.5小节,提到了几种"索引的常见执行计划":

INDEX FULL SCAN:索引的全扫描,单块读,有序
INDEX RANGE SCAN:索引的范围扫描
INDEX FAST FULL SCAN:索引的快速全扫描,多块读,无序
INDEX FULL SCAN(MIN/MAX):针对MAX(),MIN()函数的查询
INDEX SKIP SCAN:查询条件没有用到组合索引的第一列,而组合索引的第一列重复度较高时,可能用到

本文用简单的测试案例,体会下索引使用这些执行计划的场景:

1.准备测试环境

创建测试表和索引:

conn jingyu/jingyu
drop table test_objects;
create table test_objects as select * from all_objects;
create index idx_test_objects_1 on test_objects(owner, object_name, subobject_name);
create index idx_test_objects_2 on test_objects(object_id);

查看测试表结构:

SQL> desc test_objects;
Name Null? Type
----------------------------------------------------------------- -------- --------------------------------------------
OWNER NOT NULL VARCHAR2(30)
OBJECT_NAME NOT NULL VARCHAR2(30)
SUBOBJECT_NAME VARCHAR2(30)
OBJECT_ID NOT NULL NUMBER
DATA_OBJECT_ID NUMBER
OBJECT_TYPE VARCHAR2(19)
CREATED NOT NULL DATE
LAST_DDL_TIME NOT NULL DATE
TIMESTAMP VARCHAR2(19)
STATUS VARCHAR2(7)
TEMPORARY VARCHAR2(1)
GENERATED VARCHAR2(1)
SECONDARY VARCHAR2(1)
NAMESPACE NOT NULL NUMBER
EDITION_NAME VARCHAR2(30)

查看测试表上的索引信息:

SQL> select index_name, column_name, column_position from user_ind_columns where table_name = 'TEST_OBJECTS';

INDEX_NAME                     COLUMN_NAME                              COLUMN_POSITION
------------------------------ ---------------------------------------- ---------------
IDX_TEST_OBJECTS_1 OWNER 1
IDX_TEST_OBJECTS_1 OBJECT_NAME 2
IDX_TEST_OBJECTS_1 SUBOBJECT_NAME 3
IDX_TEST_OBJECTS_2 OBJECT_ID 1

分析表并清空测试环境的shared_pool和buffer_cache:

analyze table test_objects compute statistics;
alter system flush shared_pool;
alter system flush buffer_cache;

2.编写SQL语句

根据不同执行计划的场景,编写SQL语句:

--INDEX RANGE SCAN(索引的范围扫描)
SELECT owner, object_name FROM test_objects WHERE owner = 'SYS' AND object_name = 'DBMS_OUTPUT'; --INDEX SKIP SCAN(针对MAX(),MIN()函数的查询)
SELECT owner, object_name FROM test_objects WHERE object_name = 'DBMS_OUTPUT'; --INDEX FAST FULL SCAN(索引的快速全扫描,多块读,无序)
SELECT owner, object_name FROM test_objects; --INDEX FULL SCAN(索引的全扫描,单块读,有序)
SELECT owner, object_name FROM test_objects order by 1, 2; --INDEX FULL SCAN (MIN/MAX)(针对MAX(),MIN()函数的查询)
SELECT max(object_id) FROM test_objects;

3.实验环境验证

根据2中的SQL分别在实验环境中验证,没有问题,结果如下:

SQL> set autot trace
--1. INDEX RANGE SCAN
SQL> SELECT owner, object_name FROM test_objects WHERE owner = 'SYS' AND object_name = 'DBMS_OUTPUT'; Execution Plan
----------------------------------------------------------
Plan hash value: 3492129186 ---------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 29 | 3 (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| IDX_TEST_OBJECTS_1 | 1 | 29 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------------------- Predicate Information (identified by operation id):
--------------------------------------------------- 1 - access("OWNER"='SYS' AND "OBJECT_NAME"='DBMS_OUTPUT') Statistics
----------------------------------------------------------
59 recursive calls
0 db block gets
104 consistent gets
17 physical reads
0 redo size
676 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
6 sorts (memory)
0 sorts (disk)
2 rows processed --2. INDEX SKIP SCAN
SQL> SELECT owner, object_name FROM test_objects WHERE object_name = 'DBMS_OUTPUT'; Execution Plan
----------------------------------------------------------
Plan hash value: 1228438998 ---------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 58 | 27 (0)| 00:00:01 |
|* 1 | INDEX SKIP SCAN | IDX_TEST_OBJECTS_1 | 2 | 58 | 27 (0)| 00:00:01 |
--------------------------------------------------------------------------------------- Predicate Information (identified by operation id):
--------------------------------------------------- 1 - access("OBJECT_NAME"='DBMS_OUTPUT')
filter("OBJECT_NAME"='DBMS_OUTPUT') Statistics
----------------------------------------------------------
2 recursive calls
0 db block gets
32 consistent gets
23 physical reads
0 redo size
684 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
3 rows processed --3. INDEX FAST FULL SCAN
SQL> SELECT owner, object_name FROM test_objects; 84311 rows selected. Execution Plan
----------------------------------------------------------
Plan hash value: 2324984732 -------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 84311 | 387K| 138 (0)| 00:00:02 |
| 1 | INDEX FAST FULL SCAN| IDX_TEST_OBJECTS_1 | 84311 | 387K| 138 (0)| 00:00:02 |
------------------------------------------------------------------------------------------- Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
6097 consistent gets
480 physical reads
0 redo size
3509341 bytes sent via SQL*Net to client
62339 bytes received via SQL*Net from client
5622 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
84311 rows processed --4. INDEX FULL SCAN
SQL> SELECT owner, object_name FROM test_objects order by 1, 2; 84311 rows selected. Execution Plan
----------------------------------------------------------
Plan hash value: 2751381935 ---------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 84311 | 387K| 505 (1)| 00:00:07 |
| 1 | INDEX FULL SCAN | IDX_TEST_OBJECTS_1 | 84311 | 387K| 505 (1)| 00:00:07 |
--------------------------------------------------------------------------------------- Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
6090 consistent gets
0 physical reads
0 redo size
3509341 bytes sent via SQL*Net to client
62339 bytes received via SQL*Net from client
5622 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
84311 rows processed --5. INDEX FULL SCAN (MIN/MAX)
SQL> SELECT max(object_id) FROM test_objects; Execution Plan
----------------------------------------------------------
Plan hash value: 729623451 -------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 4 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 4 | | |
| 2 | INDEX FULL SCAN (MIN/MAX)| IDX_TEST_OBJECTS_2 | 1 | 4 | 2 (0)| 00:00:01 |
------------------------------------------------------------------------------------------------- Statistics
----------------------------------------------------------
2 recursive calls
0 db block gets
5 consistent gets
2 physical reads
0 redo size
534 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed

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