[20181015]为什么是3秒.txt

Posted 2021-01-13 lfree

[20181015]为什么是3秒.txt

--//以前测试:连接http://blog.itpub.net/267265/viewspace-2144765/=>为什么是12秒.txt.
--//很奇怪12.1.0.1版本测试12秒(windows版本),而11g是3秒(在使用标量子查询的情况下).不知道为什么?
--//在12.2.0.1下测试看看:

1.环境:
[email protected]> @ver1
PORT_STRING                    VERSION        BANNER                                                                               CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0           12.2.0.1.0     Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production              0

[email protected]> grant EXECUTE ON  dbms_lock to scott;
Grant succeeded.

2.建立函数:
CREATE OR REPLACE FUNCTION get_dept (p_deptno dept.deptno%TYPE)
   RETURN dept.dname%TYPE
IS
   l_dname   dept.dname%TYPE;
BEGIN
   DBMS_LOCK.sleep (1);

   SELECT dname
     INTO l_dname
     FROM dept
    WHERE deptno = p_deptno;

   RETURN l_dname;
END;
/

3.测试:
[email protected]> set timing on
[email protected]> set feedback only
[email protected]> select empno, ename, deptno, get_dept(deptno) c20 from emp;
     EMPNO ENAME          DEPTNO C20
---------- ---------- ---------- --------------------

14 rows selected.
Elapsed: 00:00:14.00
--//14秒,这是正确的,14条记录.调用14次需要14秒.

--//换成标量子查询:
[email protected]> select empno, ename, deptno, (select get_dept(deptno) from dual )c20 from emp;
     EMPNO ENAME          DEPTNO C20
---------- ---------- ---------- --------------------

14 rows selected.
Elapsed: 00:00:03.03

--//执行时间是3秒,这次是正确的,因为标量子查询缓存结果,而仅仅有3个部门在emp表.这样3秒就正确了.

4.继续探究:
[email protected]> set timing off
[email protected]> alter session set statistics_level=all;

Session altered.

[email protected]> select empno, ename, deptno, (select get_dept(deptno) from dual )c20 from emp;
     EMPNO ENAME          DEPTNO C20
---------- ---------- ---------- --------------------

14 rows selected.

[email protected]> set feedback on
[email protected]> @ dpc ‘‘ ‘‘
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  apagxtf1p2puy, child number 1
-------------------------------------
select empno, ename, deptno, (select get_dept(deptno) from dual )c20
from emp
Plan hash value: 1340320406
--------------------------------------------------------------------------------------------------------------------
| Id  | Operation         | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |      1 |        |       |     9 (100)|          |     14 |00:00:00.01 |       8 |
|   1 |  FAST DUAL        |      |      3 |      1 |       |     2   (0)| 00:00:01 |      3 |00:00:00.01 |       0 |
|   2 |  TABLE ACCESS FULL| EMP  |      1 |     14 |   182 |     3   (0)| 00:00:01 |     14 |00:00:00.01 |       8 |
--------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
   1 - SEL$2 / [email protected]$2
   2 - SEL$1 / [email protected]$1
--//从执行计划也可以发现fast dual执行了3.再次说明12.1版本有问题.
--//也再次说明oracle任何XX.1版本不能在生产系统使用.

5.继续测试使用 DETERMINISTIC Functions:
--//一般如果在在某个函数定义索引，需要DETERMINISTIC,表示返回结果固定。其实即使不固定，也可以这样定义。
CREATE OR REPLACE FUNCTION get_dept (p_deptno dept.deptno%TYPE)
   RETURN dept.dname%TYPE
   DETERMINISTIC
IS
   l_dname   dept.dname%TYPE;
BEGIN
   DBMS_LOCK.sleep (1);

   SELECT dname
     INTO l_dname
     FROM dept
    WHERE deptno = p_deptno;

   RETURN l_dname;
END;
/
[email protected]> show array
arraysize 200
--//arraysize=200

[email protected]> set timing on
[email protected]> select empno, ename, deptno, get_dept(deptno) c20  from emp;
...
14 rows selected.
Elapsed: 00:00:04.06
--//这次正确了4秒.大家可以自行设置array=2等各种情况.
--//为什么?大家可以看看我写的.http://blog.itpub.net/267265/viewspace-2138042/=>[20170426]为什么是4秒.txt

6.最后补充测试RESULT CACHE的情况:

CREATE OR REPLACE FUNCTION get_dept (p_deptno dept.deptno%TYPE)
   RETURN dept.dname%TYPE
   RESULT_CACHE
IS
   l_dname   dept.dname%TYPE;
BEGIN
   DBMS_LOCK.sleep (1);

   SELECT dname
     INTO l_dname
     FROM dept
    WHERE deptno = p_deptno;

   RETURN l_dname;
END;
/

[email protected]> select empno, ename, deptno, get_dept(deptno) c20  from emp;
14 rows selected.
Elapsed: 00:00:03.07

[email protected]> select empno, ename, deptno, get_dept(deptno) c20  from emp;
Elapsed: 00:00:00.07

--//第1次执行3秒,第2次执行0秒,因为结果缓存了.第二次执行直接取结果.修改如下结果一样.
CREATE OR REPLACE FUNCTION get_dept (p_deptno dept.deptno%TYPE)
   RETURN dept.dname%TYPE
   RESULT_CACHE
   DETERMINISTIC
IS
   l_dname   dept.dname%TYPE;
BEGIN
   DBMS_LOCK.sleep (1);

   SELECT dname
     INTO l_dname
     FROM dept
    WHERE deptno = p_deptno;

   RETURN l_dname;
END;
/

总结:
--//再次验证我以前的结论oracle 任何xx.1版本不要在生产系统使用.