Oracle 11G的DDL_LOCK_TIMEOUT参数

    今天kaums给客户做培训11g新特性,发现还真的有不少挺好的新东西,但是以前没有怎么去关注的他们,在后续的几篇中,陆续整理处理.

     DDL_LOCK_TIMEOUT specifies a time limit for how long DDL statements will wait in a DML lock queue. The default value of zero indicates a status of NOWAIT. The maximum value of 1,000,000 seconds will result in the DDL statement waiting forever to acquire a DML lock.

     If a lock is not acquired before the timeout period expires, then an error is returned.

     数据库ddl_lock_timeout参数

SQL> select * from v$version;

BANNER
---------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production

SQL> show parameter ddl_lock_timeout;

NAME                                 TYPE       VALUE
------------------------------------ ---------- --------------
ddl_lock_timeout                     integer    0

    ddl_lock_timeout默认值测试(同以前版本)

--会话1
SQL> set time on
10:27:57 SQL> create table t_xifenfei as
10:28:05   2  select * from dba_users;

Table created.

Elapsed: 00:00:00.08
10:28:17 SQL> delete from t_xifenfei where username=\'CHF\';

1 row deleted.

--会话2
SQL> set timing on
SQL> ALTER TABLE T_XIFENFEI DROP COLUMN AUTHENTICATION_TYPE;
ALTER TABLE T_XIFENFEI DROP COLUMN AUTHENTICATION_TYPE
            *
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired

Elapsed: 00:00:00.01

    设置ddl_lock_timeout超时测试

--会话1
10:28:17 SQL> delete from t_xifenfei where username=\'CHF\';

1 row deleted.

--会话2
SQL>  ALTER SESSION SET ddl_lock_timeout=10;

Session altered.

Elapsed: 00:00:00.00
SQL> ALTER TABLE T_XIFENFEI DROP COLUMN AUTHENTICATION_TYPE;
ALTER TABLE T_XIFENFEI DROP COLUMN AUTHENTICATION_TYPE
            *
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired

Elapsed: 00:00:10.01

    设置ddl_lock_timeout未超时测试

--会话2
SQL> ALTER SESSION SET ddl_lock_timeout=30;

Session altered.

Elapsed: 00:00:00.00

--会话1
10:30:00 SQL> COMMIT;

Commit complete.

Elapsed: 00:00:00.00

--会话2
SQL> ALTER TABLE T_XIFENFEI DROP COLUMN AUTHENTICATION_TYPE;

Table altered.

Elapsed: 00:00:07.91

    在以前的版本中ddl操作是nowait等待,通过实验可以发现ddl_lock_timeout可以在一定程度上解决因为我们不清楚这个表是否有dml操作而导致ddl操作不能进行的情况,从一定程度上减少了自己去尝试ddl操作,或者查询相关视图然后找出相关会话,然后kill掉对应数据的情况,可以说是在修改表结构的时候一个很不错的新特性.