关于火车站售票系统并发访问和锁机制问题？(转载)

关于火车站售票系统并发访问和锁机制问题？

如果一个用户对记录加锁，如何使其他用户看不到这条记录。
有人问到这样的问题:如果一个用户对记录加锁，如何使其他用户看不到这条记录。
此前并未注意到这样一个用法（需要8.1.7.4.16以上的版本支持）:

[oracle@jumper oracle]$ sqlplus scott/tiger

SQL*Plus: Release 9.2.0.4.0 - Production on Fri Mar 4 11:59:46 2005

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production

SQL> select * from dept;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
        33 ORACLE         beijing
        35 Oracle         Beijing
        36 Oracle         Beijing
        37 Oracle         Beijing

8 rows selected.

SQL> select * from dept where  deptno =10 for update;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK

SQL> !
[oracle@jumper oracle]$ sqlplus scott/tiger

SQL*Plus: Release 9.2.0.4.0 - Production on Fri Mar 4 12:00:14 2005

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production

SQL> select * from dept for update skip locked;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
        33 ORACLE         beijing
        35 Oracle         Beijing
        36 Oracle         Beijing
        37 Oracle         Beijing

7 rows selected.

SQL> 

 转载: http://fishforwater.itpub.net/post/27626/392849