如何获取执行计划
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发布时间：2022-04-20 05:08
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时间：2022-05-01 07:18
如何获取执行计划
来源：gdmzlhj1的专栏
如何oracle的获取执行计划
1.获取普通执行计划，效果类似于先执行set autot on exp;然后执行sql。
explan plan for your_sql;
select * from table(dbms_xplan.display);
2.获取具有outline信息的执行计划，用sqlprofile调优时非常有用，或者用这个执行计划了解更多oracle内部的hint
explan plan for your_sql;
select * from table(dbms_xplan.display(null, null,'advanced -projection'))
3.真实的执行计划，可以看到实际的 Starts（执行次数） | E-Rows（估算的返回行数） | A-Rows（实际的返回行数）
ALTER SESSION SET STATISTICS_LEVEL=ALL;
execute your_sql;
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST'))
那么这3中获取执行计划的方式可以写到一个脚本getplan.sql，用的时候非常方便。
--getplan.sql
set feedback off timing off ver off
pro 'general,outline,starts'
pro
acc type prompt 'Enter value for plan type:' default 'general'
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST')) where '&&type'='starts';
select * from table(dbms_xplan.display) where '&&type'='general';
select * from table(dbms_xplan.display(null, null,'advanced -projection')) where '&&type'='outline';
set feedback on timing on ver on
undef type
测试如下：
SQL> select * from a;
ID NAME
---------- ----------
1 a1
2 a2
3 a3
4 a4
5 a5
SQL> select * from b;
ID NAME
---------- ----------
1 b1
2 b2
--执行计划1：普通执行计划
SQL> explain plan for select a.*,(select name from b where b.id=a.id) from a;
Explained.
Elapsed: 00:00:00.04
SQL> @getplan
'general,outline,starts'
Enter value for plan type: ----这里输入general或回车
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------
Plan hash value: 3653839899
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 | 100 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| B | 1 | 20 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL| A | 5 | 100 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("B"."ID"=:B1)
Note
-----
- dynamic sampling used for this statement
--执行计划2：outline执行计划
SQL> explain plan for select a.*,(select name from b where b.id=a.id) from a;
Explained.
Elapsed: 00:00:00.01
SQL> @getplan
'general,outline,starts'
Enter value for plan type:outline --这里输入outline
PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------
Plan hash value: 3653839899
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 5 | 100 | 3 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| B | 1 | 20 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL| A | 5 | 100 | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$2 / B@SEL$2
2 - SEL$1 / A@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
FULL(@"SEL$2" "B"@"SEL$2")
FULL(@"SEL$1" "A"@"SEL$1")
OUTLINE_LEAF(@"SEL$1")
OUTLINE_LEAF(@"SEL$2")
ALL_ROWS
OPTIMIZER_FEATURES_ENABLE('10.2.0.4')
IGNORE_OPTIM_EMBEDDED_HINTS
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("B"."ID"=:B1)
Note
-----
- dynamic sampling used for this statement
--执行计划3：real执行计划
SQL> set serveroutput off
SQL> ALTER SESSION SET STATISTICS_LEVEL=ALL;
Session altered.
Elapsed: 00:00:00.00
SQL> select a.*,(select name from b where b.id=a.id) from a;
ID NAME (SELECTNAM
---------- ---------- ----------
1 a1 b1
2 a2 b2
3 a3
4 a4
5 a5
5 rows selected.
Elapsed: 00:00:00.03
SQL> @getplan
'general,outline,starts'
Enter value for plan type:starts --这里输入starts
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------
SQL_ID 8rv825dykpx1m, child number 0
-------------------------------------
select a.*,(select name from b where b.id=a.id) from a
Plan hash value: 3653839899
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
|* 1 | TABLE ACCESS FULL| B | 5 | 1 | 2 |00:00:00.01 | 35 |
| 2 | TABLE ACCESS FULL| A | 1 | 5 | 5 |00:00:00.01 | 8 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("B"."ID"=:B1)
Note
-----
- dynamic sampling used for this statement
--注意：
--第3种执行计划不能多次获取，只能执行1次，获取一次，否则会获取不到
下面再次获取一下试试：
SQL> @getplan
'general,outline,starts'
Enter value for plan type:starts
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
SQL_ID dvp8nn63wuhs8, child number 0
-------------------------------------
select * from table(dbms_xplan.display(null, null,'advanced -projection'))
where 'starts'='outline'
Plan hash value: 3440229843
-------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | A-Rows | A-Time |
-------------------------------------------------------------------------------------
|* 1 | FILTER | | 1 | 0 |00:00:00.01 |
| 2 | COLLECTION ITERATOR PICKLER FETCH| DISPLAY | 0 | 0 |00:00:00.01 | --第二次无法获取真实的执行计划
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(NULL IS NOT NULL)
Note
-----
- rule based optimizer used (consider using cbo)
--第3种执行计划要关掉set serveroutput off，否则也不能获取执行计划。
测试如下：
这里和上面的测试是同一个会话，所以没有再执行ALTER SESSION SET STATISTICS_LEVEL=ALL;了。
SQL> set serveroutput on
SQL> select a.*,(select name from b where b.id=a.id) from a;
ID NAME (SELECTNAM
---------- ---------- ----------
1 a1 b1
2 a2 b2
3 a3
4 a4
5 a5
5 rows selected.
Elapsed: 00:00:00.03
SQL> @getplan
'general,outline,starts'
Enter value for plan type:starts
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------
SQL_ID 9babjv8yq8ru3, child number 0
BEGIN DBMS_OUTPUT.GET_LINES(:LINES, :NUMLINES); END; --也无法获取真实的执行计划
NOTE: cannot fetch plan for SQL_ID: 9babjv8yq8ru3, 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_plan)
