SQL Tuning 基础概述10 - 体会索引的常见执行计划
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 | 2387K| 138 (0)| 00:00:02 |
| 1 | INDEX FAST FULL SCAN| IDX_TEST_OBJECTS_1 | 84311 | 2387K| 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 | 2387K| 505 (1)| 00:00:07 |
| 1 | INDEX FULL SCAN | IDX_TEST_OBJECTS_1 | 84311 | 2387K| 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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