oracle 03-09 数据并发

Managing Data Concurrency

Objectives
After completing this lesson, you should be able to:
• Describe the locking mechanism and how Oracle manages data concurrency
• Monitor and resolve locking conflicts

目标

完成本课程后，您应该能够：

•描述锁定机制以及Oracle如何管理数据并发性

•监控和解决锁定冲突

Locks
• Prevent multiple sessions from changing the same data at the same time
• Are automatically obtained at the lowest possible level for a given statement
• Do not escalate

锁

•防止多个会话同时更改同一数据

在给定语句的最低可能水平上自动获得

•不要升级

SQL>alter table t1 add (col2 varchar2(50));  给t1表增加一列 col2 类型为varchar2 长度为50

SQL>update t1 set col2=‘lock1‘ where col1=10;   将col1的行col2更新为lock1

SQL>insert into t1 (col1,col2) values(20,‘lock2‘);  插入一行 col1为20，col2为lock2