PostgreSQL 外键违规内部交易

Question

我有一个 function 里面有几个查询，如下所示：

CREATE OR REPLACE FUNCTION public.myfunction(winningid integer, losingid integer)
 RETURNS void
 LANGUAGE plpgsql
AS $function$
begin

update partecipants set id_be=winningId where id_be=losingId;
...
many other updates and deletes regarding other tables
...

delete from business_entity where id_be=losingId;

end;
$function$
;

参与者和business_entity之间有一个外键：

ALTER TABLE partecipants ADD CONSTRAINT partecipants_fk FOREIGN KEY (id_be) REFERENCES business_entity(id_be)

有时（如千分之一）此 function 挂起并出现错误：

error: update or delete on table "business_entity" violates foreign key constraint "partecipants_fk" on table "partecipants"
detail:
   'Key (id_be)=(315017) is still referenced from table "partecipants".

如果我第二次运行相同的 function ，则结束没有错误。

这怎么可能？

作为背景信息，其他进程在运行时正在使用（通常也带有锁）function 中涉及的表。

Answer 1

并发事务可以在您的UPDATE和您的DELETE之间添加或修改partecipants中的行，以便后者失败。

如果您想避免这种情况，请在一个语句中执行这两项操作：

WITH dummy AS (
   update partecipants set id_be=winningId where id_be=losingId
)
delete from business_entity where id_be=losingId;