• Oracle外键不加索引会引起死锁问题


    转载链接:http://www.jb51.net/article/50161.htm

    这篇文章主要介绍了Oracle外键不加索引引起死锁的情况及解决,需要的朋友可以参考下

    --创建一个表,此表作为子表

    create table fk_t as select * from user_objects;

    delete from fk_t where object_id is null;

    commit;

    --创建一个表,此表作为父表

    create table pk_t as select * from user_objects;

    delete from pk_t where object_id is null;

    commit;

    --创建父表的主键

    alter table PK_t add constraint pk_pktable primary key (OBJECT_ID);

    --创建子表的外键

    alter table FK_t add constraint fk_fktable foreign key (OBJECT_ID) references pk_t (OBJECT_ID);

    --session1:执行一个删除操作,这时候在子表和父表上都加了一个Row-S(SX)锁

    delete from fk_t where object_id=100;

    delete from pk_t where object_id=100;

    --session2:执行另一个删除操作,发现这时候第二个删除语句等待

    delete from fk_t where object_id=200;

    delete from pk_t where object_id=200;

    --回到session1:死锁马上发生

    delete from pk_t where object_id=100;

    session2中报错:

    SQL> delete from pk_table where object_id=200;
    delete from pk_table where object_id=200
    *
    第 1 行出现错误:

    ORA-00060: 等待资源时检测到死锁

    当对子表的外键列添加索引后,死锁被消除,因为这时删除父表记录不需要对子表加表级锁。

    --为外键建立索引

    create index ind_pk_object_id on fk_t(object_id) nologging;

    --重复上面的操作session1

    delete from fk_t where object_id=100;

    delete from pk_t where object_id=100;

    --session2

    delete from fk_t where object_id=200;

    delete from pk_t where object_id=200;

    --回到session1不会发生死锁

    delete from pk_t where object_id=100; 



    关于外键不加索引引起死锁的详细分析参考http://blog.csdn.net/robinson1988/article/details/38421991


    经过验证,如果外键不加索引的确会出现死锁。因此,外键务必添加索引。


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  • 原文地址:https://www.cnblogs.com/wenlong/p/5255665.html
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