Question

关于锁定表格，这两个语句有何不同之处：

-- Variation 1

BEGIN TRAN

-- Lock the table explicitly via a SELECT
DECLARE @TempId BIGINT=(SELECT TOP(1) Id FROM TargetTable WITH (TABLOCKX, HOLDLOCK));

-- Then perform DML operations
MERGE TargetTable as target
USING (...) AS source
ON (target.Id=source.Id)
WHEN MATCHED THEN
  DELETE
WHEN NOT MATCHED THEN
  INSERT ... ;

DELETE FROM Target
WHERE Id=...

COMMIT TRAN

与：相比：

-- Variation 2

BEGIN TRAN

-- Lock the table as part of the first DML operation
MERGE TargetTable WITH (TABLOCKX, HOLDLOCK) as target
USING (...) AS source
ON (target.Id=source.Id)
WHEN MATCHED THEN
  DELETE
WHEN NOT MATCHED THEN
  INSERT ... ;

DELETE FROM Target
WHERE Id=...

COMMIT TRAN

在这两种情况下，同一个表都会使用TABLOCKX，但是对于Variation 2，当多个会话同时执行此代码时，我会遇到死锁。对于变体1，我没有。我认为这两种方法的工作方式相同，但显然锁定TABLOCKX的方式或保持时间有所不同。

有些知识渊博的人请对此有所了解。

TABLOCKX，HOLDLOCK范围问题

0 个答案: