SqlDataReader索引器性能

Question

我有一些像這樣的代碼：

using (var cmd = TransicsCommand.GetFleetCommand())
{
    cmd.CommandText = @"
                        SELECT dr.DeviceId, dr.DeviceTruckRelationId, dr.TruckId, dr.RelationCreatedOn,
                        dl.DriverLoginId, dl.DriverId, dl.UserType, dl.LoginType, dl.SecondsSince DriverLoginCreated,
                        Action.ActionId, Action.ActionTimestamp, Action.UserType actionusertype, Action.TripreportId,
                        DeviceHeaderData.DeviceHeaderid, DeviceHeaderData.Odo, DeviceHeaderData.X, DeviceHeaderData.Y,
                        DeviceHeaderData.ValidPosition, DeviceHeaderData.Tfu,
                        DeviceHeaderData.FuelPercentage, DeviceHeaderData.Speed, 
                        InstructionsetAction.VersionId,
                        tc.CouplingId, tc.TrailerId, tc.CouplingEvent, tc.TrailerEntry, tc.SecondsSince
                        FROM TripReport.Action Action
                        INNER JOIN DeviceHeader.Data DeviceHeaderData ON Action.DeviceHeaderId = DeviceHeaderData.DeviceHeaderId
                        INNER JOIN Instructionset.Action InstructionsetAction  ON InstructionsetAction.ActionId = Action.ActionId
                        INNER JOIN DeviceHeader.Truck dht ON Action.DeviceHeaderId = dht.DeviceHeaderId
                        INNER JOIN Device.TruckRelation dr ON dht.DeviceRelationId = dr.DeviceTruckRelationId 
                        LEFT OUTER JOIN [DeviceHeader].[LoginSession] dhls ON dhls.DeviceHeaderId = dht.DeviceHeaderId
                        LEFT OUTER JOIN [LogIn].DriverLogin as dl ON dhls.DriverLoginId = dl.DriverLoginId
                        LEFT OUTER JOIN [DeviceHeader].[TrailerCoupling] dhtc ON dhtc.DeviceHeaderId = dht.DeviceHeaderId
                        LEFT OUTER JOIN [Trailer].[Coupling] as tc ON dhtc.CouplingId = tc.CouplingId ";

    using (var reader = cmd.ExecuteReader())
    {
        while (reader.Read())
        {   
            Stopwatch sw = new Stopwatch();
            sw.Start();
            var trailerId = reader["TrailerId"];
            sw.Stop();
            Debug.WriteLine(trailerId + "-" + sw.ElapsedMilliseconds);//10s - 8s -...
        }
    }
}

此代碼需要40秒。 經過一番搜索后，我發現規則閱讀器[“TrailerId”]總共需要39 秒 ，查詢本身運行速度非常快！

刪除“TC”。 來自“TrailerId”的標題使其以0.6秒運行，讀者[“TrailerId”]現在只需要0ms：

SELECT ..., tc.CouplingId, TrailerId,...

這是sqldatareader索引器代碼中的錯誤嗎？ 我無法理解為什么第二個版本的工作速度比第一個版本快得多。

Answer 1

嘗試將“TrailerId”列的索引從循環中取出並在內部使用; afaik它使這個數字在記錄中尋找每個，例如

using (var reader = cmd.ExecuteReader())
{
    int idx = -1;
    while (reader.Read())
    {   
        if (idx==-1) idx = reader.GetOrdinal("TrailerId");
        Stopwatch sw = new Stopwatch();
        sw.Start();
        var trailerId = reader[idx];
        sw.Stop();
        Debug.WriteLine(trailerId + "-" + sw.ElapsedMilliseconds);//10s - 8s -...
    }
}

Answer 2

使用序數索引並且不要每次都聲明變量。
使用特定於數據類型的方法。
假設trailerID是Int32和位置22。

Stopwatch sw = new Stopwatch();
Int32 trailerID;
while (reader.Read())
{   
    sw.Start();
    trailerId = reader.GetInt(22);
    sw.Stop();
    Debug.WriteLine(trailerId + "-" + sw.ElapsedMilliseconds);//10s - 8s -...
}

同
var trailerId = reader [“TrailerId”];
它必須找到TrailerId並為每個循環分配正確的數據類型。

不確定為什么TC會有所作為。
最有可能的事情與找到它，然后模式分配var。