Sql server 调度应用程序的并发问题

我们的应用程序需要一个简单的调度机制——我们只能在同一时间间隔内为每个房间安排一次访问，但一次访问可以使用一个或多个房间。使用SQL Server 2005，示例过程可能如下所示：

CREATE PROCEDURE CreateVisit
    @start datetime, @end datetime, @roomID int
AS
BEGIN
DECLARE @isFreeRoom INT

BEGIN TRANSACTION

SELECT @isFreeRoom = COUNT(*) 
FROM visits V
INNER JOIN visits_rooms VR on VR.VisitID = V.ID
WHERE @start = start AND @end = [end] AND VR.RoomID = @roomID

IF (@isFreeRoom = 0)
BEGIN
    INSERT INTO visits (start, [end]) VALUES (@start, @end)
    INSERT INTO visits_rooms (visitID, roomID) VALUES (SCOPE_IDENTITY(), @roomID)
END

COMMIT TRANSACTION
END

WHERE [start] < @end AND [end] > @start AND RoomID = @roomID

---

为了不让同一个房间同时安排两次参观，我们应该如何在程序上处理这个问题？我们应该使用可序列化事务隔离级别还是使用表提示锁？哪一个更好？

我以前做过这个

。。。

---

锁将在事务结束时释放。

我会让调用应用程序在房间ID的逗号分隔列表中传递，并在SQL中拆分它们，一次插入插入所有行。这样做，在一次选择上使用正确的锁定提示，应该可以让您的计划过程正常工作

，但如果有拆分方法，则可以使用自己的拆分方法。下面是如何使数字表拆分方法起作用：

要使此方法起作用，您需要执行以下一次性时间表设置：

SELECT TOP 10000 IDENTITY(int,1,1) AS Number
    INTO Numbers
    FROM sys.objects s1
    CROSS JOIN sys.objects s2
ALTER TABLE Numbers ADD CONSTRAINT PK_Numbers PRIMARY KEY CLUSTERED (Number)

设置数字表后，创建此拆分函数：

CREATE FUNCTION [dbo].[FN_ListToTable]
(
     @SplitOn  char(1)      --REQUIRED, the character to split the @List string on
    ,@List     varchar(8000)--REQUIRED, the list to split apart
)
RETURNS TABLE
AS
RETURN 
(

    ----------------
    --SINGLE QUERY-- --this will not return empty rows
    ----------------
    SELECT
        ListValue
        FROM (SELECT
                  LTRIM(RTRIM(SUBSTRING(List2, number+1, CHARINDEX(@SplitOn, List2, number+1)-number - 1))) AS ListValue
                  FROM (
                           SELECT @SplitOn + @List + @SplitOn AS List2
                       ) AS dt
                      INNER JOIN Numbers n ON n.Number < LEN(dt.List2)
                  WHERE SUBSTRING(List2, number, 1) = @SplitOn
             ) dt2
        WHERE ListValue IS NOT NULL AND ListValue!=''

);
GO 

输出：

ListValue
-----------------------
1
2
3
4
5
6777

(6 row(s) affected)

这就是我将为您制定的程序：

CREATE PROCEDURE CreateVisit
    @start datetime, @end datetime, @roomIDs varchar(8000)
AS
BEGIN
DECLARE @RowID INT

BEGIN TRANSACTION

IF NOT EXISTS (SELECT
                   1
                   FROM visits_rooms           (HOLDLOCK,UPDLOCK)  v 
                       INNER JOIN dbo.FN_ListToTable(',',@roomIDs) r ON v.RoomID=r.ListValue
                   WHERE @start = start AND @end = [end] AND VR.RoomID = @roomID --copy of your logic, but shouldn't it be WHERE start>=@start AND [end]<=@end
              )
BEGIN
    INSERT INTO visits (start, [end]) VALUES (@start, @end)
    SELECT @RowID=SCOPE_IDENTITY()
    INSERT INTO visits_rooms
            (visitID, roomID)
        SELECT 
            @RowID, r.ListValue
            FROM dbo.FN_ListToTable(',',@roomIDs) r

END

COMMIT TRANSACTION
END

去

如果您有多个Roomid一次计划尝试，您可以首先将它们拆分为@TENTRABLE变量或实际表TENTRABLE，然后在if EXISTS和INSERT SELECT中重用它们

其中@start=start和@end=[end]以及VR.RoomID=@RoomID

此检查不正确，因为您只会发现房间的日程安排正好在@start和@end之间。如果房间安排在@start-1、@end或@start、@end+1之间，也就是说，任何与您想要的开始和结束不完全匹配的重叠间隔，您会发现房间是“空闲”的。正确的检查如下所示：

CREATE PROCEDURE CreateVisit
    @start datetime, @end datetime, @roomID int
AS
BEGIN
DECLARE @isFreeRoom INT

BEGIN TRANSACTION

SELECT @isFreeRoom = COUNT(*) 
FROM visits V
INNER JOIN visits_rooms VR on VR.VisitID = V.ID
WHERE @start = start AND @end = [end] AND VR.RoomID = @roomID

IF (@isFreeRoom = 0)
BEGIN
    INSERT INTO visits (start, [end]) VALUES (@start, @end)
    INSERT INTO visits_rooms (visitID, roomID) VALUES (SCOPE_IDENTITY(), @roomID)
END

COMMIT TRANSACTION
END

WHERE [start] < @end AND [end] > @start AND RoomID = @roomID

---

不是对您问题的回答，但您应该使用范围\标识而不是@标识

UPDATE TOP(@numberOfRooms) RoomHours WITH (ROWLOCK, READPAST)
 SET Free = 0
OUTPUT DELETED.RoomID
WHERE Free = 1
AND RoomHour BETWEEN @start AND @end;