SELECT和UPDATE表，所以没有线程的重叠 [英] SELECT and UPDATE table so there is no overlap of Threads

问题描述

说我有如下表：

ID|Read
-------
 1|true
 2|false
 3|false
 4|false

...我需要阅读的最小ID，已[阅读] ==虚假; 。再加上，更新了我现在读

... and I need to read the smallest ID, that has [Read] == false; plus, update that I have now read it.

所以，如果我执行我的存储过程dbo.getMinID，它将返回ID：2，和更新[阅读] - >真实的。

So if i execute my Stored Procedure dbo.getMinID, it will return ID: 2, and update [Read] -> true.

CREATE PROCEDURE [dbo].[getMinID]
(
  @QueryID INT OUTPUT 
)
BEGIN
  SELECT TOP 1 @QueryID = [ID] from Table
  UPDATE Table SET [Read] = 1 WHERE [ID] = @QueryID 
END

的问题是，我有十（10）执行dbo.getMinID，同时异步线程，和我不能让他们选择在任何情况下相同的[ID]。我很担心，第二个线程我的我的SELECT和UPDATE语句之间执行，从而回到[ID]：在这两种情况下2

The problem is that I have ten (10) asynchronous Threads executing dbo.getMinID, at the same time, and I CANNOT have them select the SAME [ID] under any circumstances. I am worried that a second thread my execute between my SELECT and UPDATE statement, thus returning [ID]: 2 in both scenarios.

我怎么能保证我不选择/更新相同的记录两次，无论有多少个线程在存储过程行事？另外，请记住，表不变地增加新行，所以我不能锁表！

How can I ensure that I do not select/update the same record twice, no matter how many threads are acting upon the Stored Procedure? ALSO, please keep in mind that the table CONSTANTLY has new rows added, so I cannot lock the table!

推荐答案

如果你的意思并发安全队列类型的锁定，然后使用ROWLOCK，UPDLOCK，READPAST提示？

If you mean a concurrency safe queue type locking, then use ROWLOCK, UPDLOCK, READPAST hints?

的 SQL Server进程队列竞争状态

BEGIN TRAN

SELECT TOP 1 @QueryID = [ID] from Table WITH (ROWLOCK, UPDLOCK, READPAST)
UPDATE Table SET [Read] = 1 WHERE [ID] = @QueryID 

COMMIT TRAN -- TRAM

然而，在一个声明。像

WITH T AS
(
    --ORDER BY with TOP , or perhaps MIN is better?
    SELECT TOP 1 [Read], [ID] from Table
    WITH (ROWLOCK, UPDLOCK, READPAST) ORDER BY [Read]
)
UPDATE
    T
SET
    [Read] = 1;

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