异步查询数据库怎么能花0个节拍呢?

我试图使用IDbInterceptor来计时实体框架的查询执行，尽可能准确，实现乔纳森·艾伦对类似问题的回答的变体:

public class PerformanceLogDbCommendInterceptor : IDbCommandInterceptor
{
    static readonly ConcurrentDictionary<DbCommand, DateTime> _startTimes =
            new ConcurrentDictionary<DbCommand, DateTime>();
    public void ReaderExecuted(DbCommand command,
            DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        Log(command, interceptionContext);
    }
    public void NonQueryExecuted(DbCommand command,
            DbCommandInterceptionContext<int> interceptionContext)
    {
        Log(command, interceptionContext);
    }
    public void ScalarExecuted(DbCommand command,
            DbCommandInterceptionContext<object> interceptionContext)
    {
        Log(command, interceptionContext);
    }
    private static void Log<T>(DbCommand command,
            DbCommandInterceptionContext<T> interceptionContext)
    {
        DateTime startTime;
        TimeSpan duration;
        if(!_startTimes.TryRemove(command, out startTime))
        {
            //Log exception
            return;
        }
        DateTime now = DateTime.UtcNow;
        duration = now - startTime;
        string requestGUID = Guid.Empty.ToString();
        var context = interceptionContext.DbContexts.SingleOrDefault();
        if (context == null)
        {
            //Log Exception
        }
        else
        {
            var businessContext = context as MyDb;
            if (businessContext == null)
            {
                //Log Exception
            }
            else
            {
                requestGUID = businessContext.RequestGUID.ToString();
            }
        }
        string message;
        var parameters = new StringBuilder();
        foreach (DbParameter param in command.Parameters)
        {
            parameters.AppendLine(param.ParameterName + " " + param.DbType
                + " = " + param.Value);
        }
        if (interceptionContext.Exception == null)
        {
            message = string.Format($"Database call took"
                + $" {duration.TotalMilliseconds.ToString("N3")} ms."
                + $" RequestGUID {requestGUID}"
                //+ $" 'r'nCommand:'r'n{parameters.ToString() + command.CommandText}");
        }
        else
        {
            message = string.Format($"EF Database call failed after"
                + $" {duration.TotalMilliseconds.ToString("N3")} ms."
                + $" RequestGUID {requestGUID}"
                + $" 'r'nCommand:'r'n{(parameters.ToString() + command.CommandText)}"
                + $"'r'nError:{interceptionContext.Exception} ");
        }
        if (duration == TimeSpan.Zero)
        {
            message += $" 'r'nTime: start: {startTime.ToString("hh:mm:ss fffffff")}"
                + $" | now: {now.ToString("hh:mm:ss fffffff")}"
                + $" 'r'n 'r'nCommand:'r'n"
                + $"{parameters.ToString() + command.CommandText}";
        }
        System.Diagnostics.Debug.WriteLine(message);
    }

    public void NonQueryExecuting(DbCommand command,
            DbCommandInterceptionContext<int> interceptionContext)
    {
        OnStart(command);
    }
    public void ReaderExecuting(DbCommand command,
            DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        OnStart(command);
    }
    public void ScalarExecuting(DbCommand command,
            DbCommandInterceptionContext<object> interceptionContext)
    {
        OnStart(command);
    }
    private static void OnStart(DbCommand command)
    {
        _startTimes.TryAdd(command, DateTime.UtcNow);
    }
}

奇怪的是，每10个左右的查询，它需要0个tick来执行。它似乎只发生在我异步运行它时，同时有几个查询。另一件需要注意的事情是，当我再次查询相同的查询时，并不总是相同的查询需要0个滴答。

此外，我目前正在测试的数据库位于本地网络上，而不是本地机器上- ping时间为0-1ms -所以即使数据被缓存，我也看不出它如何花费0个ticks。

值得注意的是，大多数查询花费的时间可疑地接近1,2,3 ms(例如0.997ms到1.003ms)。对我来说，这听起来像是操作系统旋转线程cpu时间和/或1ms睡眠。我不介意它发生了，但我只是想知道为什么，这样我就可以解释结果中的不准确之处了。

这可能与ConcurrentDictionary有关。但是当我现在测试时，我目前只调用异步(WCF)方法一次，等待每个异步DB调用，所以它甚至不应该一次触发更多的调用，据我的理解。这是一个叫做:

的例子

public async Task<IEnumerable<DTJobAPPOverview>> GetJobOverviewAsync()
    ...
    var efResponsibleUserFullName = await dbContext.tblUsers.Where(u =>
                u.UserID == efJob.ResponsibleUserID
            ).Select(u => u.FullName)
            .FirstOrDefaultAsync();
    dtJob.ResponsibleUserName = efResponsibleUserName;
    var efCase = await dbContext.tblCases.FirstOrDefaultAsync(c =>
            c.ID == efJob.FK_CaseID);
    dtJob.Case = Mapper.Map<DTCase>(efCase); //Automapper
    ...
}

顺便说一下，我知道我可能应该转换整个应用程序来使用导航属性，但这是我们目前所拥有的，所以请原谅我。