Linq to SQL：查詢在SQL Server Management Studio中運行良好，但在應用程序上超時

Question

我正在維護舊版應用程序的代碼。 它正在使用Entity Framework 3.5，目前無法將其更新為較新版本。

最近有一個查詢開始超時。 這是LINQ中的查詢：

var compoQueryResult = (from composition in MyAppDataContext.Compositions
                            join compositionStatus in MyAppDataContext.CompositionStatus on composition.StatusID equals compositionStatus.CompositionStatusID
                            join compoUnit in MyAppDataContext.CompositionUnits on composition.CompositionID equals compoUnit.CompositionID
                            join unit in MyAppDataContext.Units on compoUnit.UnitID equals unit.UnitID
                            join carUnit in MyAppDataContext.Car_Units on unit.UnitID equals carUnit.UnitId
                            join car in MyAppDataContext.Cars on carUnit.CarId equals car.CarID
                            join location in MyAppDataContext.Locations on unit.ParkedLocationID equals location.LocationID
                            from road in MyAppDataContext.Roads.Where(r => r.RoadID == unit.RoadID).DefaultIfEmpty()
                            from ta in MyAppDataContext.Allocations.Where(ta => ta.CompositionId == composition.CompositionID).DefaultIfEmpty()
                            from arrivalLocation in MyAppDataContext.Locations.Where(al => al.LocationID == ta.EndLocationID).DefaultIfEmpty()
                            where (MyApp.IsAdministrator || MyApp.GetLineIds().Contains(car.LineId.Value))
                            && car.LineId.Value == LineId                           
                            && (statusId == null || statusId == compositionStatus.CompositionStatusID)
                            && (locationId == null || unit.ParkedLocationID == locationId)
                            && (!onlyATMS.HasValue
                                 || (onlyATMS == true && composition.CompositionName.Contains(Common.Constants.ATMSSymbol))
                                 || (onlyATMS == false && !composition.CompositionName.Contains(Common.Constants.ATMSSymbol)))
                            select new CompositionQueryResultItem
                            {
                                CompositionId = composition.CompositionID,
                                CompositionName = composition.CompositionName,
                                CompositionNumber = composition.CompositionNumber,
                                DateTimeModified = composition.DataModified,
                                Status = compositionStatus.CompositionStatusDesc,
                                Location = location.LocationName,
                                Road = road.Name,
                                Number = ta.Number,
                                DepartureTime = ta.DepartTime,
                                ArrivalLocation = arrivalLocation.LocationName,
                                ArrivalTime = ta.ArriveTime
                            }).Distinct().ToList();

調試應用程序后，我可以看到正在執行以下查詢：

SELECT DISTINCT [t10].[CompositionID] AS [CompositionId], [t10].[CompositionName], [t10].[CompositionNumber], [t10].[value] AS [DateTimeModified], [t10].[CompositionStatusDesc] AS [Status], [t10].[LocationName] AS [Location], [t10].[value2] AS [Road], [t10].[value3] AS [Number], [t10].[value4] AS [DepartureTime], [t10].[value5] AS [ArrivalLocation], [t10].[value6] AS [ArrivalTime]
FROM (
    SELECT [t0].[CompositionID], [t0].[CompositionName], [t0].[CompositionNumber], [t0].[DataModified] AS [value], [t1].[CompositionStatusDesc], [t6].[LocationName], [t7].[Name] AS [value2], [t8].[Number] AS [value3], [t8].[DepartTime] AS [value4], [t9].[LocationName] AS [value5], [t8].[ArriveTime] AS [value6], [t5].[LineId]
    FROM [dbo].[Composition] AS [t0]
    INNER JOIN [dbo].[CompositionStatus] AS [t1] ON [t0].[StatusID] = [t1].[CompositionStatusID]
    INNER JOIN [dbo].[CompositionUnit] AS [t2] ON [t0].[CompositionID] = [t2].[CompositionID]
    INNER JOIN [dbo].[Unit] AS [t3] ON [t2].[UnitID] = [t3].[UnitID]
    INNER JOIN [dbo].[Car_Unit] AS [t4] ON [t3].[UnitID] = [t4].[UnitId]
    INNER JOIN [dbo].[Car] AS [t5] ON [t4].[CarId] = [t5].[CarID]
    INNER JOIN [dbo].[Location] AS [t6] ON [t3].[ParkedLocationID] = ([t6].[LocationID])
    LEFT OUTER JOIN [dbo].[Road] AS [t7] ON ([t7].[RoadID]) = [t3].[RoadID]
    LEFT OUTER JOIN [dbo].[Allocation] AS [t8] ON [t8].[CompositionId] = ([t0].[CompositionID])
    LEFT OUTER JOIN [dbo].[Location] AS [t9] ON [t9].[LocationID] = [t8].[EndLocationID]
    ) AS [t10]
WHERE ([t10].[LineId]) = @p0

如果我在SQL Server Manager Studio上執行該查詢，則不會有任何問題。 它在不到一秒鍾的時間內執行。 但是，該應用程序正在超時，我不知道為什么。

我試着做

MyAppDataContext.ObjectTrackingEnabled = false;

但我仍然遇到相同的錯誤。

我將放棄並創建一個存儲過程，但是我無法理解為什么會發生超時。

Answer 1

當通過應用程序運行同一查詢時，SQL Server使用的查詢執行計划可以不同。 檢查您的執行計划。 您可以在查詢結束時使用諸如option（recompile）之類的提示，也可以針對特定的Lineid優化它（如果對於不同的id，返回的行明顯不同）。 有時，使用此類提示會使SSMS變慢，但在應用程序中卻不會變慢。 經過一番嘗試后，您可以找到解決方案。