ORA-12838: cannot read/modify an object after modifying it in parallel

今天涛神说程序报ORA-12838错误，调出程序sql发现是一个大批量的insert，里面使用了
/*+ append */的hint，于是下面做了段模拟这个错误实验

session 1

SQL> create table tb_test as select * from emp where 1=2;

Table created.

SQL> insert /*+ append */ into tb_test select * from emp;

14 rows created.  -- 注意/*+ append*/ 没有commit

SQL> select * from tb_test;
select * from tb_test
*
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel

session 2

SQL> select * from tb_test;

no rows selected

session 1 报了ORA-12838的错误，session正常，说明了在同一个事物中如果使用/*+ append */ insert如果没有commit去做dml操作会这个错误，

进一步查询发现表上加了类型为6的锁

SQL> col object_name for a20;
SQL> select t2.object_name,t1.LOCKED_MODE from  v$locked_object t1 join dba_objects t2 on t1.OBJECT_ID = t2.object_id;

OBJECT_NAME	     LOCKED_MODE
-------------------- -----------
TB_TEST 		       6

我们知道 locked mode 6： Lock table t in exclusive mode， 排他锁限制最高的TM锁，会禁止执行任何类型的DML语句