执行计划display_cursor函数

问题描述：关于oracle查看真实的执行计划，使用select * from table(dbms_xplan.display_cursor(null,null));的方式来获取执行计划

参考文档：https://blog.csdn.net/leshami/article/details/6866925

一、display_cursor描述

display_cursor用于显示SQL语句的真实的执行计划

DISPLAY_CURSOR语法

         DBMS_XPLAN.DISPLAY_CURSOR(
            sql_id        IN  VARCHAR2  DEFAULT  NULL,
            child_number  IN  NUMBER    DEFAULT  NULL,
            format        IN  VARCHAR2  DEFAULT  'TYPICAL');

display_cursor函数参数描述

        sql_id

                指定位于库缓存执行计划中SQL语句的父游标。默认值为null。当使用默认值时当前会话的最后一条SQL语句的执行计划将被返回可以通过查询V$SQL 或 V$SQLAREA的SQL_ID列来获得SQL语句的SQL_ID。

        child_number

                指定父游标下子游标的序号。即指定被返回执行计划的SQL语句的子游标。默认值为0。如果为null，则sql_id所指父游标下所有子游标的执行计划都将被返回。

        format

                控制SQL语句执行计划的输出部分，即哪些可以显示哪些不显示。使用与display函数的format参数与修饰符在这里同样适用。
                除此之外当在开启statistics_level=all时或使用gather_plan_statistics提示可以获得执行计划中实时的统计信息
                有关详细的format格式描述请参考：dbms_xplan之display函数的使用 中format参数的描述

        下面给出启用统计信息时format新增的修饰符

                iostats   控制I/O统计的显示
                last      默认，显示所有执行计算过的统计。如果指定该值，则只显示最后一次执行的统计信息
                memstats  控制pga相关统计的显示
                allstats  此为iostats memstats的快捷方式，即allstats包含了iostats和memstats
                run_stats_last 等同于iostats last。只能用于oracle 10g R1
                run_stats_tot  等同于iostats。只能用于oracle 10g R1

二、使用scott用户演示使用display_cursor函数获取执行计划

1、当前数据库版本以及加载执行计划到库缓存

SQL> show user
USER is "SCOTT"
SQL> select * from v$version where rownum<2; 

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

SQL>
SQL> SELECT ename,dname,loc
FROM   emp e, dept d
WHERE  e.deptno = d.deptno
AND    e.empno  = 7788;   2    3    4  

ENAME	   DNAME	  LOC
---------- -------------- -------------
SCOTT	   RESEARCH	  DALLAS

2、查看真实的执行计划，不传递任何参数给display_cursor函数，显示当前会话最后一条SQL语句的执行计划

SQL> select * from table(dbms_xplan.display_cursor(null,null));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	a67wqmkfb9j65, child number 0
-------------------------------------
SELECT ename,dname,loc FROM   emp e, dept d WHERE  e.deptno = d.deptno
AND    e.empno	= 7788

Plan hash value: 2385808155

----------------------------------------------------------------------------------------
| Id  | Operation		     | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |	       |       |       |     2 (100)|	       |
|   1 |  NESTED LOOPS		     |	       |     1 |    54 |     2	 (0)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID| EMP     |     1 |    24 |     1	 (0)| 00:00:01 |
|*  3 |    INDEX UNIQUE SCAN	     | PK_EMP  |     1 |       |     0	 (0)|	       |
|   4 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    30 |     1	 (0)| 00:00:01 |
|*  5 |    INDEX UNIQUE SCAN	     | PK_DEPT |     1 |       |     0	 (0)|	       |
----------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - access("E"."EMPNO"=7788)
   5 - access("E"."DEPTNO"="D"."DEPTNO")

24 rows selected.

3.获得SQL语句的SQL_ID，可以看出此SQL_ID与上面显示的执行计划中的SQL_ID一致

SQL> select sql_id,address,plan_hash_value,hash_value,child_number from v$sql
where sql_text like '%SELECT ename%' and sql_text not like '%from v$sql%'; 2

SQL_ID	ADDRESS	PLAN_HASH_VALUE HASH_VALUE CHILD_NUMBER
------------- ---------------- --------------- ---------- ------------
a67wqmkfb9j65 0000000072C8C9D8	2385808155 2629092549	0

4.传递SQL_ID以及format参数，并配合修饰符控制执行计划的输出

/*--------------  ------------------------*/

SQL> select * from table(dbms_xplan.display_cursor('a67wqmkfb9j65',null,'typical -predicate -rows'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	a67wqmkfb9j65, child number 0
-------------------------------------
SELECT ename,dname,loc FROM emp e, dept d WHERE e.deptno = d.deptno
AND e.empno	= 7788

Plan hash value: 2385808155

--------------------------------------------------------------------------------
| Id | Operation	| Name | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT	|	| | 2 (100)|	|
| 1 | NESTED LOOPS	|	| 54 | 2	(0)| 00:00:01 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 24 | 1	(0)| 00:00:01 |
| 3 | INDEX UNIQUE SCAN	| PK_EMP | | 0	(0)|	|
| 4 | TABLE ACCESS BY INDEX ROWID| DEPT | 30 | 1	(0)| 00:00:01 |
| 5 | INDEX UNIQUE SCAN	| PK_DEPT | | 0	(0)|	|
--------------------------------------------------------------------------------

18 rows selected.

　　

scott用户遇到的问题一：User has no SELECT privilege on V$SESSION

SQL> r
1* select * from table(dbms_xplan.display_cursor(null,null))

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
User has no SELECT privilege on V$SESSION

解决：

grant select on v_$sql to scott;
grant select on v_$sql_plan to scott;
grant select on v_$session to scott;
grant select on v_$sql_plan_statistics_all to scott;

问题二：cannot fetch plan for SQL_ID: 372mc93u1j1yk

SQL> r
1* select * from table(dbms_xplan.display_cursor(null,null))

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
SQL_ID 372mc93u1j1yk, child number 0

select * from table(dbms_xplan.display_cursor(null,null))

NOTE: cannot fetch plan for SQL_ID: 372mc93u1j1yk, CHILD_NUMBER: 0
Please verify value of SQL_ID and CHILD_NUMBER;
It could also be that the plan is no longer in cursor cache (check v$sql_p
lan)

解决：

SQL> set serveroutput off;
SQL> show serveroutput
serveroutput OFF

5.执行上述SQL语句后获得其真实的执行计划，使用了iostats last -predicate -note 修饰符控制显示输出

SQL> alter session set statistics_level=all;

Session altered.

SQL> select e.ename,e.sal,s.grade
from emp e
join salgrade s             2    3
on e.sal between losal and hisal
and e.deptno = 20;  4    5  

ENAME		  SAL	   GRADE
---------- ---------- ----------
SMITH		  800	       1
JONES		 2975	       4
SCOTT		 3000	       4
ADAMS		 1100	       1
FORD		 3000	       4

SQL> select * from table(dbms_xplan.display_cursor(null,null,'iostats last -predicate -note'));
SQL_ID	243b0tpjxj6wv, child number 1
-------------------------------------
select e.ename,e.sal,s.grade from emp e join salgrade s on e.sal
between losal and hisal and e.deptno = 20

Plan hash value: 4204027666

-------------------------------------------------------------------------------------------
| Id | Operation	| Name	| Starts | E-Rows | A-Rows | A-Time	| Buffers |
-------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT |	| 1 |	|	5 |00:00:00.01 | 13 |
| 1 | MERGE JOIN	|	| 1 |	1 |	5 |00:00:00.01 | 13 |
| 2 | SORT JOIN	|	| 1 |	5 |	5 |00:00:00.01 |	6 |
| 3 | TABLE ACCESS FULL | EMP	| 1 |	5 |	5 |00:00:00.01 |	6 |
| 4 | FILTER	|	| 5 |	|	5 |00:00:00.01 |	7 |
| 5 | SORT JOIN	|	| 5 |	5 |	14 |00:00:00.01 |	7 |
| 6 | TABLE ACCESS FULL| SALGRADE | 1 |	5 |	5 |00:00:00.01 |	7 |
-------------------------------------------------------------------------------------------

19 rows selected.

6.修改会话级别的参数statistics_level为typical并验证修改结果，scott用户无v$parameter权限可以用sys

SQL> col name format a40
col value format a25
col display_value format aSQL> SQL> 25
select name, value, display_value, isses_modifiable
from v$parameter                                    SQL>   2
where isses_modifiable = 'TRUE'
and name like '%&input_name%';     3    4
Enter value for input_name: statistics_level
old   4: and name like '%&input_name%'
new   4: and name like '%statistics_level%'

NAME					 VALUE			   DISPLAY_VALUE	     ISSES
---------------------------------------- ------------------------- ------------------------- -----
statistics_level			 TYPICAL		   TYPICAL		     TRUE

7.使用提示gather_plan_statistics，并获得其真实执行计划，使用了allstats -rows修饰符控制显示输出

SQL> set pagesize 180
SELECT /*+ gather_plan_statistics */ ename,dname,loc
FROM   emp e, dept d      SQL>   2
WHERE  e.deptno = d.deptno
AND    d.deptno=20 ORDER BY 1,2,3;    3    4  

ENAME	   DNAME	  LOC
---------- -------------- -------------
ADAMS	   RESEARCH	  DALLAS
FORD	   RESEARCH	  DALLAS
JONES	   RESEARCH	  DALLAS
SCOTT	   RESEARCH	  DALLAS
SMITH	   RESEARCH	  DALLAS

SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstats -rows'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	d2hh42yzqqjz7, child number 0
-------------------------------------
SELECT /*+ gather_plan_statistics */ ename,dname,loc FROM   emp e, dept
d WHERE  e.deptno = d.deptno AND    d.deptno=20 ORDER BY 1,2,3

Plan hash value: 3339094711

---------------------------------------------------------------------------------------------------------------------
| Id  | Operation		      | Name	| Starts | A-Rows |   A-Time   | Buffers |  OMem |  1Mem |  O/1/M   |
---------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	      | 	|      1 |	5 |00:00:00.01 |       8 |	 |	 |	    |
|   1 |  SORT ORDER BY		      | 	|      1 |	5 |00:00:00.01 |       8 |  2048 |  2048 |     1/0/0|
|   2 |   NESTED LOOPS		      | 	|      1 |	5 |00:00:00.01 |       8 |	 |	 |	    |
|   3 |    TABLE ACCESS BY INDEX ROWID| DEPT	|      1 |	1 |00:00:00.01 |       2 |	 |	 |	    |
|*  4 |     INDEX UNIQUE SCAN	      | PK_DEPT |      1 |	1 |00:00:00.01 |       1 |	 |	 |	    |
|*  5 |    TABLE ACCESS FULL	      | EMP	|      1 |	5 |00:00:00.01 |       6 |	 |	 |	    |
---------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   4 - access("D"."DEPTNO"=20)
   5 - filter("E"."DEPTNO"=20)

24 rows selected.