[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.