Question

以下sproc尝试将一行插入表中并生成随机ID，该ID用于相应表上的PK。在catch块中处理与随机生成的ID的冲突，其中重试/再次调用该过程。现在，这需要很长时间并导致死锁，因为锁会保持很长一段时间。有没有办法在重试之前立即释放死锁，以便在其他线程成功锁定PK索引时有一个短窗口？


CREATE PROCEDURE addPerson
    (
        @FirstName nvarchar(100),
        @LastName nvarchar(100)
    )
AS
BEGIN
    SET NOCOUNT ON;

    DECLARE @PersonId int

    -- generate random PersonId
    -- this sproc can generate ids that already exist in the table
    EXEC generateRandomPersonId @PersonId=@PersonId OUTPUT

    BEGIN TRY       
        INSERT INTO [dbo].[Persons] 
        (
            PersonId,FirstName,LastName
        )
        VALUES 
        (
            @PersonId,@FirstName,@LastName
        )

    BEGIN CATCH
        -- 
        -- HOW TO RELEASE LOCKS HERE that are still held
        -- for the previous INSERT statement?
        --

        DECLARE @ErrorNumber int, @ErrorMessage nvarchar(2048)
        SELECT  @ErrorNumber=ERROR_NUMBER(), 
                @ErrorMessage=ERROR_MESSAGE()

        -- if a race condition happened and 
        -- PersonId happened to be picked already, retry all over again
        IF (@ErrorNumber = 2601 OR @ErrorNumber = 2627 AND CHARINDEX(N'PK_Persons_PersonId', @ErrorMessage) > 0)
            BEGIN
               --
               -- RETRYING HERE participates in a high possibility and 
               -- occurrence of deadlocks
               -- 
               EXEC addPerson @FirstName,@LastName
            END
            ELSE 
               -- some other error, rethrow it
               EXEC rethrowError
            END
    END CATCH
END
GO

Answer 1

进程不会阻塞自己的锁。由于对存储过程的调用在同一进程中运行，因此第二个insert无法等待第一个insert的锁定。

你能发布一个死锁图吗？这显示了有关阻止过程的大量信息。

作为一个快速解决方案，你可以在一个循环中搜索一个免费的ID，这可以避免大多数（但不是全部）可能的冲突：

while 1=1
    begin
    EXEC generateRandomPersonId @PersonId=@PersonId OUTPUT
    if not exists (select * from Persons where PersonId = @PersonID)
        break
    end

Answer 2

首先，我希望这个程序只适用于学术环境，而不适用于商业产品或真实生产环境。

这是一种方法：

通过循环替换递归
使用交易

CREATE PROCEDURE addPerson
    (
        @FirstName nvarchar(100),
        @LastName nvarchar(100)
    )
AS

BEGIN
  SET NOCOUNT ON;

  DECLARE @doed bit

  set @doed = 0

  DECLARE @PersonId int

  WHILE @doed = 0

  BEGIN
    -- generate random PersonId
    -- this sproc can generate ids that already exist in the table
    EXEC generateRandomPersonId @PersonId=@PersonId OUTPUT

    BEGIN TRANSACTION ExceptionHandling
    BEGIN TRY       

            INSERT INTO [dbo].[Persons] 
            (
                PersonId,FirstName,LastName
            )
            VALUES 
            (
                @PersonId,@FirstName,@LastName
            )
            COMMIT TRANSACTION ExceptionHandling
        BEGIN CATCH

            ROLLBACK TRANSACTION ExceptionHandling
            -- 
            -- HOW TO RELEASE LOCKS HERE that are still held
            -- for the previous INSERT statement?
            --

            DECLARE @ErrorNumber int, @ErrorMessage nvarchar(2048)
            SELECT  @ErrorNumber=ERROR_NUMBER(), 
                    @ErrorMessage=ERROR_MESSAGE()

                        -- if a race condition happened and 
            -- PersonId happened to be picked already, retry all over again
            IF !(@ErrorNumber = 2601 OR @ErrorNumber = 2627 AND CHARINDEX(N'PK_Persons_PersonId', @ErrorMessage) > 0)
                BEGIN
                   --
                   -- RETRYING HERE participates in a high possibility and 
                   -- occurrence of deadlocks
                   set @doed = 0
                END
                ELSE 
                   -- some other error, rethrow it
                   set @doed = 1
                   EXEC rethrowError
                END
        END CATCH
  END  --end while
 END
GO

免责声明：未经测试

由重试的INSERT引起的死锁

2 个答案: