发现了一个隐含参数_disable_cursor_sharing 可以用来禁止游标的共享，不过这个隐含参数没有什么意义，
违背了ORACLE尽量游标共享的理念。
下面看一下这个参数的作用：
SQL> show parameter disable_cursor_sharing
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
_disable_cursor_sharing boolean TRUE
SQL> variable id number
SQL> exec :id:=1;
PL/SQL procedure successfully completed.
SQL> select * from t where id=:id;
no rows selected
SQL> select sql_text,executions from v$sql where sql_text='select * from t where id=:id';
SQL_TEXT EXECUTIONS
------------------------------ ----------
select * from t where id=:id 1
SQL> exec :id:=2;
PL/SQL procedure successfully completed.
SQL> select * from t where id=:id;
no rows selected
SQL> select sql_text,executions from v$sql where sql_text='select * from t where id=:id';
SQL_TEXT EXECUTIONS
------------------------------ ----------
select * from t where id=:id 1
select * from t where id=:id 1
仅供参考。
