问题描述：
SQL> altersession enable parallel dml;
ERROR:
ORA-12841: 无法变更事务处理中的会话并行 DML 状态
解决:
1、查找dml lock的锁的sid
SQL> select session_id, owner,name,MODE_HELD fromsys.dba_dml_locks;
SESSION_ID OWNER NAME MODE_HELD
------------------------------------------------------------------------------------------------------------------------------------------------------------
373SCOTT T_DRIVEWAYDATA Row-X(SX)
245SCOTT T_DRIVEWAYDATA Row-X(SX)
373SYS SEQ$ Row-X (SX)
124SYS PLAN_TABLE$ Row-X(SX)
126 SCOTT T_DRIVEWAYDATA Row-X(SX)
363SCOTT T_DRIVEWAYDATA Row-X (SX)
已选择6行。
2、依据上文找到sid，查询锁住的sql语句
SQL> selectb.sql_text from v$session a,v$sqlarea b where a.sql_hash_value=b.hash_value anda.sid='126';
SQL_TEXT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
----------------
SELECT T_DRIVEWAYDATA_SEQUENCE.NEXTVAL FROM DUAL
原来此时SID为126的session正在对表T_DRIVEWAYDATA进行INSERT操作，而表中有一个自增的主键。