我已在下表中,與的EntityFramework 6.1製作:爲什麼我使用我製作的索引時查詢速度較慢?
CREATE TABLE [dbo].[MachineryReading] (
[Id] INT IDENTITY (1, 1) NOT NULL,
[Location] [sys].[geometry] NULL,
[Latitude] FLOAT (53) NOT NULL,
[Longitude] FLOAT (53) NOT NULL,
[Altitude] FLOAT (53) NULL,
[Odometer] INT NULL,
[Speed] FLOAT (53) NULL,
[BatteryLevel] INT NULL,
[PinFlags] BIGINT NOT NULL,
[DateRecorded] DATETIME NOT NULL,
[DateReceived] DATETIME NOT NULL,
[Satellites] INT NOT NULL,
[HDOP] FLOAT (53) NOT NULL,
[MachineryId] INT NOT NULL,
[TrackerId] INT NOT NULL,
[ReportType] NVARCHAR (1) NULL,
[FixStatus] INT DEFAULT ((0)) NOT NULL,
[AlarmStatus] INT DEFAULT ((0)) NOT NULL,
[OperationalSeconds] INT DEFAULT ((0)) NOT NULL,
CONSTRAINT [PK_dbo.MachineryReading] PRIMARY KEY CLUSTERED ([Id] ASC),
CONSTRAINT [FK_dbo.MachineryReading_dbo.Machinery_MachineryId] FOREIGN KEY ([MachineryId]) REFERENCES [dbo].[Machinery] ([Id]) ON DELETE CASCADE,
CONSTRAINT [FK_dbo.MachineryReading_dbo.Tracker_TrackerId] FOREIGN KEY ([TrackerId]) REFERENCES [dbo].[Tracker] ([Id]) ON DELETE CASCADE
);
GO
CREATE NONCLUSTERED INDEX [IX_MachineryId]
ON [dbo].[MachineryReading]([MachineryId] ASC);
GO
CREATE NONCLUSTERED INDEX [IX_TrackerId]
ON [dbo].[MachineryReading]([TrackerId] ASC);
那是一個大量的信息,而我們最常見(最慢)的查詢只使用它的一個子集:
SELECT TOP 1 OperationalSeconds
FROM MachineryReading
WHERE MachineryId = @id
AND DateRecorded > @start
AND DateRecorded < @end
AND OperationalSeconds <> 0
的表存儲了幾百萬行,從大約2012年開始記錄,儘管我們的代碼設置爲從2000年開始進行一些搜索。它的運行速度非常緩慢,因此我使用的一個人根據DateRecorded對錶格進行了分區:
ALTER PARTITION SCHEME PartitionSchemeMonthRange NEXT USED [Primary]
ALTER PARTITION FUNCTION [PartitionFunctionMonthRange]() SPLIT RANGE(N'2016-01-01T00:00:00.000')
ALTER PARTITION SCHEME PartitionSchemeMonthRange NEXT USED [Primary]
ALTER PARTITION FUNCTION [PartitionFunctionMonthRange]() SPLIT RANGE(N'2016-02-01T00:00:00.000')
...
CREATE UNIQUE CLUSTERED INDEX [PK_dbo.MachineryReadingPs] ON MachineryReading(DateRecorded, Id) ON PartitionSchemeMonthRange(DateRecorded)
但是,上面的查詢仍然運行緩慢。所以,最重要的是,我做了另一個指標:
CREATE NONCLUSTERED INDEX [IX_MachineryId_DateRecorded]
ON [dbo].[MachineryReading]([DateRecorded] ASC, [MachineryId] ASC)
INCLUDE([OperationalSeconds], [FixStatus]);
再次執行該查詢,執行計劃表明它完全無視我剛纔提出的指標,轉而選擇固定掃描和索引上IX_MachineryId求。這在很短的日期範圍內工作很快,但對於獲得總運行時間非常可怕。我可以處理:WITH(INDEX(IX_MachineryId_DateRecorded))
。
沒有。它實際上運行顯着較慢,當使用我專門爲該查詢製作的索引!是什麼賦予了?我能做些什麼更好?
爲什麼您在索引中將MachineryId前的DateRecorded?我會以相反的方式做到這一點 –
嘗試索引'(MachineryID,DateRecorded)'。擁有它的順序應該使它對優化器更有利。 *(您使用的順序會將所有內容按時間順序排列,建議順序會將所有內容按機器順序排列。)* – MatBailie
這是我的拼寫錯誤 - 我將它命名爲IX_MachineryId_DateRecorded,它應該按照該順序排列。這可以解釋很多... –