[20181015]为什么是3秒.txt
[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:
SCOTT@test01p> @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
SYS@test01p> 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:
SCOTT@test01p> set timing on
SCOTT@test01p> set feedback only
SCOTT@test01p> 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:
SCOTT@test01p> 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:
SCOTT@test01p> set timing off
SCOTT@test01p> alter session set statistics_level=all;
Session altered.
SCOTT@test01p> select empno, ename, deptno, (select get_dept(deptno) from dual )c20 from emp;
EMPNO ENAME DEPTNO C20
---------- ---------- ---------- --------------------
14 rows selected.
SCOTT@test01p> set feedback on
SCOTT@test01p> @ 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 / DUAL@SEL$2
2 - SEL$1 / EMP@SEL$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;
/
SCOTT@test01p> show array
arraysize 200
--//arraysize=200
SCOTT@test01p> set timing on
SCOTT@test01p> 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;
/
SCOTT@test01p> select empno, ename, deptno, get_dept(deptno) c20 from emp;
14 rows selected.
Elapsed: 00:00:03.07
SCOTT@test01p> 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.
