sql - 行锁 - 手动使用它们

Question

我基本上有一个应用程序，它有 5 个线程，每个线程都从一个表中读取。查询是一个简单的 SELECT TOP 1 * from the table，但我想强制锁定，以便下一个线程将从表中选择下一条记录，而不是锁定的记录。当应用程序完成它的任务时，它将更新锁定的记录并释放锁定并再次重复该过程。这可能吗？

Answer 1

我推荐的方法是在记录中设置一个字段，指示是否正在处理记录。然后实现执行以下操作的“从队列中读取下一个”sproc，以确保没有 2 个进程获取相同的记录:

BEGIN TRANSACTION

-- Find the next available record that's not already being processed.
-- The combination of UPDLOCK and READPAST hints makes sure 2 processes don't 
-- grab the same record, and that processes don't block each other.
SELECT TOP 1 @ID = ID
FROM YourTable WITH (UPDLOCK, READPAST)
WHERE BeingProcessed = 0

-- If we've found a record, set it's status to "being processed"
IF (@ID IS NOT NULL)
    UPDATE YourTable SET BeingProcessed = 1 WHERE ID = @ID

COMMIT TRANSACTION

-- Finally return the record we've picked up
IF (@ID IS NOT NULL)
    SELECT * FROM YourTable WHERE ID = @ID

有关这些表提示的更多信息，请参阅 MSDN