重試INSERT引起的死鎖

Question

以下sproc嘗試向表中插入一行並生成隨機ID，該ID用於相應表上的PK。在catch塊中處理隨機生成的ID的衝突，在該塊中再次重試/調用該過程。現在，這需要很長時間，並導致死鎖，因爲鎖定會保留很長一段時間。有沒有辦法在重試之前立即釋放死鎖，以便在其他線程可以成功鎖定PK索引時出現一個短窗口？

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

進程不會阻塞自己的鎖。由於對存儲過程的調用在相同的進程中運行，因此第二個insert不可能等待第一個insert的鎖定。

你能發佈死鎖圖嗎？這顯示了關於阻塞過程的大量信息。

作爲速戰速決，您可以搜索在一個循環中游離的ID，這將避免大多數（但不是全部）可能的衝突：

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

Answer 2

首先，我希望這個程序只適用在學術環境中，而不是在商業產品或實際生產環境中。

這是一個方法：

• 由循環替換遞歸
• 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​ 

免責聲明：沒有測試