关于ORACLE中ORA-00054: 资源正忙, 但指定以 NOWAIT 方式获取资源

同时对一个表操作,update,truncate 等操作，会造成此错误，另外，事物没有提交，从而进行其他操作也有可能会造成此异常。

ORA-00054 resource busy and acquire with NOWAIT specified

Cause: The NOWAIT keyword forced a return to the command prompt because a resource was unavailable for a LOCK TABLE or SELECT FOR UPDATE command.

Action: Try the command after a few minutes or enter the command without the NOWAIT keyword.

原因:对表进行相关操作时，该表被锁定，或表正在被其他程序占用，导致系统忙。

解决:对表解锁或等待完成。

比如当我修改表的某一记录时候，没有commit，并又去修改表结构，则会触发此异常。

异常信息: ORA-00054: 资源正忙, 但指定以 NOWAIT 方式获取资源

异常demo：

Let's try to produce the problem in our development environment. I have opened two session that connected to database under a schema. In one session, I have created a table and inserted data into it.

SQL> create table a (a number);

Table created.

SQL> insert into a values(1);

1 row created.

I did not yet committed data in session 1. Now in another session whenever I try to any ddl like (alter table, drop table) ORA-00054 will produce.

In another session,
SQL> alter table a add b number;
alter table a add b number
*
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified


SQL> drop table a;
drop table a
*
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified

SQL> lock table a in exclusive mode nowait;
lock table a in exclusive mode nowait
*
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified


Cause of the Problem
Whenever you try to do any structural changes on a table oracle try to lock the table exclusively with NOWAIT option(this is in 10.2g while in 11g you can change the wait timeout). If oracle fails to lock the table exclusively then ORA-00054 will occur.

Solution of the Problem
In 10.2g you are limited to several choices to solve the problem. To avoid it,

-Re run the DDL at a later time when the database become idle.
or,

-Kill the sessions that are preventing the exclusive lock.
or,

-Prevent end user to connect to the database and then run the DDL.

You have different views to see locking information about the table.
1)DBA_BLOCKERS: Displays a session if it is not waiting for a locked object but is holding a lock on an object for which another session is waiting. In our scenario this view will not help.

2)DBA_DDL_LOCKS: It lists all DDL locks held in the database and all outstanding requests for a DDL lock.

3)DBA_DML_LOCKS: It lists all DML locks held in the database and all outstanding requests for a DML lock.
If you query from it in the mode_held field you will see 'row exclusive lock'.
SQL> select mode_held from dba_dml_locks where owner='MAXIMSG';

MODE_HELD
-------------
Row-X (SX)

4)DBA_LOCK: It lists all locks or latches held in the database, and all outstanding requests for a lock or latch.

5)DBA_LOCK_INTERNAL: It displays a row for each lock or latch that is being held, and one row for each outstanding request for a lock or latch.

6)DBA_LOCKS is a synonym for DBA_LOCK.

7)DBA_WAITERS: Shows all the sessions that are waiting for a lock.

In order to see locked object query,