Oracle 变量之 DDL_LOCK_TIMEOUT

你的名字 2021-03-18 14:33 624阅读 0赞

DDL\_LOCK\_TIMEOUT  
Property Description  
Parameter type Integer  
Default value 0  
Modifiable ALTER SESSION  
Range of values 0 to 1,000,000 (in seconds)  
Basic No

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.

该参数是oralce 11g中才有的；

实验：

\--session 1

SQL> select \* from v$version;  
BANNER  
\--------------------------------------------------------------------------------  
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production  
PL/SQL Release 11.2.0.1.0 - Production  
CORE    11.2.0.1.0      Production  
TNS for Linux: Version 11.2.0.1.0 - Production  
NLSRTL Version 11.2.0.1.0 - Production

SQL> show parameter ddl  
NAME                                 TYPE        VALUE  
\------------------------------------ ----------- ------------------------------  
ddl\_lock\_timeout                     integer     0  
enable\_ddl\_logging                   boolean     FALSE

\--session 2

SQL> insert into t\_1 values('b');  
1 row created.

\--session 3

SQL> alter table t\_1 modify(a varchar2(50));  
alter table t\_1 modify(a varchar2(50))  
            \*  
ERROR at line 1:  
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired  
该错误是执行之后没有等待直接出现；

\--session 1

SQL> alter system set ddl\_lock\_timeout=60;  
System altered.

SQL> show parameter ddl  
NAME                                 TYPE        VALUE  
\------------------------------------ ----------- ------------------------------  
ddl\_lock\_timeout                     integer     60  
enable\_ddl\_logging                   boolean     FALSE

\--session 2

SQL> insert into t\_1 values('a');  
1 row created.

\--session 3

SQL> alter table t\_1 modify (a varchar2(30));  
alter table t\_1 modify (a varchar2(30))  
            \*  
ERROR at line 1:  
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired

该错误是在等待了60秒之后才出现；

\--session 3

SQL> alter table t\_1 add  c number;

则会一直等待下去，直到请求的锁资源被释放（该变量不起作用）；

在网上有些文章说，如果是添加列回立即提交，不敢苟同；