我对ORACLE数据锁的一点体会

该贴的部分内容是针对帖中带的附件(一位大侠关于锁的理解),提的理解/疑问, 


大家在读此贴前,请先阅读该文。 


先说说各类型的锁:共享锁,排它说,共享排它锁(对表定义共享,对表操作的记录排它)。 


1、我对文章中意向锁的理解,就是:对表的记录进行操作之前,先对表定义(包括表结构、约束等) 


 加了共享锁,这是为了避免对表的DDL操作。 


 比如:当你往TAB1插入一条记录时,该表的一个字段COL8是允许为空的,插入这条记录的该字段 


 的值是空的,此时,若不对该表定义加共享锁,则另外一SESSION对TAB1.COL8加非空约束, 


 那该表结构修改就与插入的记录发生冲突了。所以,当执行DML操作是,必定对操作的表加DDL 


 共享锁。 


 这是我理解的意向锁。 

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