当表上存在外键时发生死锁

Question

DB，Audit和AuditField中存在两个表，以下是Create表代码：

-- Primary key: ID
CREATE TABLE [dbo].[Audit](
[ID] [int] IDENTITY(1,1) NOT NULL PRIMARY KEY,
[TypeName] [varchar](50) NOT NULL
) 
GO

-- Primary key: ID
CREATE TABLE [dbo].[AuditField](
[ID] [int] IDENTITY(1,1) NOT NULL PRIMARY KEY,
[AuditID] [int] NOT NULL,
[Field1] [varchar](50) NOT NULL
)

GO
-- Set foreign key on AuditField table 
ALTER TABLE [dbo].[AuditField] 
ADD  CONSTRAINT [FK_AuditFiled_Audit] FOREIGN KEY([AuditID])
REFERENCES [dbo].[Audit] ([ID])
GO

然后我准备了一些测试数据：

DECLARE @audit TABLE
(
ID int not null,
TypeName varchar(50)
)

DECLARE @auditField TABLE
(
AuditID int not null,
Field1 varchar(50)
)

-- ADD TEST DATA
DECLARE @i int = 1
DECLARE @rowCount int = 500
WHILE @i<=@rowCount
BEGIN
INSERT INTO @audit
VALUES(@i, 'SomeTypeName')

INSERT INTO @auditField
(AuditID,Field1)
VALUES(@i,'SomeThing')

SET @i += 1
END

最后，我运行以下事务将测试数据插入这两个表：

begin transaction
INSERT INTO dbo.Audit
SELECT TypeName
FROM @audit
ORDER BY ID

declare @lastIdentity int = @@identity
declare @offSet int = @lastIdentity - @rowCount

INSERT INTO dbo.AuditField
SELECT AuditID+@offSet AS AuditID, Field1
FROM @auditField 
ORDER BY AuditID
commit transaction

当此事务并发运行时，发生死锁，一个进程失败，另一个进程出错：

  

消息547，级别16，状态0，行40 INSERT语句冲突   使用FOREIGN KEY约束“FK_AuditFiled_Audit”。冲突   发生在数据库“MyDB”，表“dbo.Audit”，列'ID'。

Audit和AuditField表上没有触发器。 很抱歉代码的格式，我真的需要一个答案，为什么会发生这种死锁，谢谢。

有一件事应该是清楚的，AuditField表的数据来自@auditField，As @Bogdan回答我改写如下：

begin transaction
INSERT INTO dbo.Audit
OUTPUT inserted.ID INTO @temp
SELECT TypeName
FROM @audit

INSERT INTO @idMapping
SELECT ROW_NUMBER() OVER(ORDER BY ID) AS RowNumber, ID
FROM @temp

INSERT INTO dbo.AuditField
SELECT m.ID AS AuditID, Field1
FROM @auditField af
INNER JOIN @idMapping m ON af.AuditID = m.RowNumber

commit transaction

Answer 1

这是和读 - 写死锁：

如您所见，每个事务都已成功获取[e] X [clusive]锁，并且它会请求S [hared]锁。问题是为什么事务尝试读取由另一个事务锁定的行X.

答案如下： 1）以下一段源代码

declare @lastIdentity int = @@identity
declare @offSet int = @lastIdentity - @rowCount

假设每个

生成IDENTITY个值

INSERT INTO dbo.Audit
SELECT TypeName
FROM ...

声明仍在继续。这完全错了，如下图所示：

这意味着在某个时间点，事务可以成功地在插入的行上获得X锁定然后 1）因为插入审计的行不是连续的 2）因为

declare @lastIdentity int = @@identity
declare @offSet int = @lastIdentity - @rowCount

INSERT INTO dbo.AuditField
SELECT AuditID+@offSet AS AuditID, Field1 ...

这最后INSERT尝试插入属于另一个事务的dbo.AuditField，AuditID值，这需要FK验证，并且还意味着SQL Server需要从dbo.Audit读取行。对于这个S [hared]需要锁。

要明确：此死锁的根本原因不是FK约束。真正的问题是源代码。

解决方案：我会改写：

begin transaction
INSERT INTO dbo.Audit
OUTPUT inserted.ID, inserted.TypeName INTO @audit (ID, TypeName)
SELECT TypeName
FROM @audit
-- ORDER BY ID -- Isn't necessary 

... do something (ex. DELETE) with rows from @audit

INSERT INTO dbo.AuditField (AuditID, ...)
SELECT x.ID, ...
FROM @audit x
-- ORDER BY AuditID 

/* or 
    INSERT INTO dbo.AuditField (AuditID, Field1, ....)
    SELECT y.ID, y.ColumnName, ...
    FROM (
        SELECT x.ID, ...
        FROM @audit x
        UNPIVOT( ColumnValue FOR ColumnName IN ([TypeName], ...) )
    ) y
    WHERE y.....
*/
commit transaction -- Isn't necessary

Answer 2

您正在尝试将无效的外键值插入dbo.AuditField：

SELECT AuditID+@offSet AS AuditID, Field1

为何选择@offset？您不一定在dbo.Audit表中使用具有该值的AuditId。