Gather more plan statistics by gather_plan

在10g以后我们可以通过利用gather_plan_statistics提示来了解更多的SQL执行统计信息，具体使用方法如下：

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SQL> set linesize 150

SQL> set pagesize 2000

SQL> set autotrace traceonly exp

SQL> select avg(SALARY),DEPARTMENT_NAME from

employees e,departments d where e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME;

Execution Plan

----------------------------------------------------------

Plan hash value: 3294250112

---------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 27 | 621 | 5 (20)| 00:00:01 |

| 1 | HASH GROUP BY | | 27 | 621 | 5 (20)| 00:00:01 |

| 2 | NESTED LOOPS | | 106 | 2438 | 4 (0)| 00:00:01 |

| 3 | TABLE ACCESS FULL | EMPLOYEES | 107 | 749 | 3 (0)| 00:00:01 |

| 4 | TABLE ACCESS BY INDEX ROWID| DEPARTMENTS | 1 | 16 | 1 (0)| 00:00:01 |

|* 5 | INDEX UNIQUE SCAN | DEPT_ID_PK | 1 | | 0 (0)| 00:00:01 |

---------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

5 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")

SQL> show parameter cursor_sharing

NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

cursor_sharing string EXACT

SQL> show parameter statistics_level

NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

statistics_level string TYPICAL

SQL> set autotrace off;

SQL> select /*+ gather_plan_statistics */ avg(SALARY),DEPARTMENT_NAME from

employees e,departments d where e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME;

SQL> select * from TABLE(dbms_xplan.display_cursor(NULL,NULL,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT

------------------------------------------------------------------------------------------------------------------------------------------------------

SQL_ID bctzu9xuxay18, child number 0

-------------------------------------

select /*+ gather_plan_statistics */ avg(SALARY),DEPARTMENT_NAME from employees e,departments d

where e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME

Plan hash value: 3294250112

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

| 1 | HASH GROUP BY | | 1 | 27 | 11 |00:00:00.01 | 219 |

|   2 |   NESTED LOOPS            |         |      1 |    106 |    106 |00:00:00.01 |     219 |

| 3 | TABLE ACCESS FULL | EMPLOYEES | 1 | 107 | 107 |00:00:00.01 | 7 |

| 4 | TABLE ACCESS BY INDEX ROWID| DEPARTMENTS | 107 | 1 | 106 |00:00:00.01 | 212 |

|* 5 | INDEX UNIQUE SCAN | DEPT_ID_PK | 107 | 1 | 106 |00:00:00.01 | 106 |

-------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

5 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")

/* 可以从starts列看到某种操作执行了多少次，例如这里的INDEX UNIQUE SCAN为107次 */

/*也可以通过SQL_ID来定位计划信息 */

SQL> select t.*

from v$sql s

, table(dbms_xplan.display_cursor(s.sql_id,s.child_number,'ALL IOSTATS LAST')) t where s.sql_id = '&SQL_ID' ;

Enter value for sql_id: bctzu9xuxay18

old 3: , table(dbms_xplan.display_cursor(s.sql_id,s.child_number,'ALL IOSTATS LAST')) t where s.sql_id = '&SQL_ID'

new 3: , table(dbms_xplan.display_cursor(s.sql_id,s.child_number,'ALL IOSTATS LAST')) t where s.sql_id = 'bctzu9xuxay18'

PLAN_TABLE_OUTPUT

------------------------------------------------------------------------------------------------------------------------------------------------------

SQL_ID bctzu9xuxay18, child number 0

-------------------------------------

select /*+ gather_plan_statistics */ avg(SALARY),DEPARTMENT_NAME from

employees e,departments d where

e.DEPARTMENT_ID=d.DEPARTMENT_ID group by DEPARTMENT_NAME

Plan hash value: 3294250112

---------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------------------------------

| 1 | HASH GROUP BY

|         |      1 |     27 |   621 |     5  (20)| 00:00:01 |     11 |00:00:00.01 |     219 |

|   2 |   NESTED LOOPS            |         |      1 |    106 |  2438 |     4   (0)| 00:00:01 |    106 |00:00:00.01 |     219 |

| 3 | TABLE ACCESS FULL

| EMPLOYEES   |      1 |    107 |   749 |     3   (0)| 00:00:01 |    107 |00:00:00.01 |       7 |

| 4 | TABLE ACCESS BY INDEX

ROWID| DEPARTMENTS |    107 |      1 |    16 |     1   (0)| 00:00:01 |    106 |00:00:00.01 |     212 |

|* 5 | INDEX UNIQUE

SCAN         | DEPT_ID_PK  |    107 |      1 |       |     0   (0)|          |    106 |00:00:00.01 |     106 |

---------------------------------------------------------------------------------------------------------------------------------------

Query Block Name / Object Alias (identified by operation id):

-------------------------------------------------------------

1 - SEL$1

3 - SEL$1 / E@SEL$1

4 - SEL$1 / D@SEL$1

5 - SEL$1 / D@SEL$1

Predicate Information (identified by operation id):

---------------------------------------------------

5 - access("E"."DEPARTMENT_ID"="D"."DEPARTMENT_ID")

Column Projection Information (identified by operation id):

-----------------------------------------------------------

1 - "DEPARTMENT_NAME"[VARCHAR2,30], AVG("SALARY")[22]

2 - "SALARY"[NUMBER,22], "DEPARTMENT_NAME"[VARCHAR2,30]

3 - "SALARY"[NUMBER,22], "E"."DEPARTMENT_ID"[NUMBER,22]

4 - "DEPARTMENT_NAME"[VARCHAR2,30]

5 - "D".ROWID[ROWID,10]

SQL> alter session set statistics_level=ALL;

Session altered.

/* 在session级别设置statistics_level为ALL,可以为我们提供更为详尽的执行统计信息 */

本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1277730

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