Oracle外鍵不加索引會引起死鎖問題

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這篇文章主要介紹了Oracle外鍵不加索引引起死鎖的情況及解決,需要的朋友可以參考下

--創建一個表，此表作爲子表

create table fk_t as select * from user_objects;

delete from fk_t where object_id is null;

commit;

--創建一個表，此表作爲父表

create table pk_t as select * from user_objects;

delete from pk_t where object_id is null;

commit;

--創建父表的主鍵

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

--創建子表的外鍵

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

--session1:執行一個刪除操作，這時候在子表和父表上都加了一個Row-S(SX)鎖

delete from fk_t where object_id=100;

delete from pk_t where object_id=100;

--session2:執行另一個刪除操作，發現這時候第二個刪除語句等待

delete from fk_t where object_id=200;

delete from pk_t where object_id=200;

--回到session1:死鎖馬上發生

delete from pk_t where object_id=100;

session2中報錯：

SQL> delete from pk_table where object_id=200;
delete from pk_table where object_id=200
*
第 1 行出現錯誤:

ORA-00060: 等待資源時檢測到死鎖

當對子表的外鍵列添加索引後，死鎖被消除，因爲這時刪除父表記錄不需要對子表加表級鎖。

--爲外鍵建立索引

create index ind_pk_object_id on fk_t(object_id) nologging;

--重複上面的操作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不會發生死鎖

delete from pk_t where object_id=100; 

關於外鍵不加索引引起死鎖的詳細分析參考http://blog.csdn.net/robinson1988/article/details/38421991

經過驗證，如果外鍵不加索引的確會出現死鎖。因此，外鍵務必添加索引。