清空共享池和数据库缓冲区缓存

场景1：
select * from emp where empno=7934;

update emp set sal = sal * 1.1 where empno=7934;

场景2：
alter system flush shared_pool;
alter system flush buffer_cache;
alter system flush global context;

select * from emp where empno=7934;

alter system flush shared_pool;

update emp set sal = sal * 1.1 where empno=7934;

场景3：

alter system flush shared_pool;
alter system flush buffer_cache;
alter system flush global context;

update emp set sal = sal * 1.1 where empno=7934;