Question

我被要求做一个系统，该系统每秒轮询一次数据库中的一个表，如果它反对符合条件的行开始处理该行的动作。

我已经做到了这一点，但我时不时地得到一个例外。我有一个WPF应用程序，我有一个在后台运行的线程。该线程有一个循环，并在循环结束时休眠一秒钟。与“数据库”的连接在“using”子句中打开。

以下是我的主题：

Private Sub PollDatabase()
    While m_StopThread = False
      Try
        Dim listOfRows As List(Of DataObject) = db.GetDataObjects()

        ... Do something with the rows ...

       Catch ex As Exception
          m_log.WriteLine(ex.ToString())
       End Try
    Thread.Sleep(1000)
    End While
End Sub

我的SQL函数如下所示：

Public Function GetDataObjects() As List(Of DataObject)
  Dim result As New List(Of DataObject)
  Dim sb As New StringBuilder("... the sql query ...")

     Using cnn = New SqlConnection(_connectionString)
         cnn.Open()
         Using cmd = New SqlCommand(sb.ToString(), cnn)
          cmd.CommandTimeout = 0
          Using DataReader As SqlDataReader = cmd.ExecuteReader()
            Do While DataReader.Read()
              ... read the columns from table 
                  to the dataobject ...
              result.Add(DataObject)
            Loop
          End Using
        End Using
     End Using
  Return result
End Function

现在似乎随机的我的日志有一个超时异常：

System.Data.SqlClient.SqlException (0x80131904): Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
...
at System.Data.SqlClient.SqlConnection.Open()

我的问题是：这是否可以节省这样做？或者我在这里做了一些根本错误的事情？当然，如果有人有建议解决这个问题。

编辑：

我尝试了一些与SQL函数不同的方法。我现在在应用程序启动时打开一个连接并转储“using”子句。所以我的函数现在看起来像这样：

Public Function GetDataObjects() As List(Of DataObject)
  Dim result As New List(Of DataObject)
  Dim sb As New StringBuilder("... the sql query ...")
  _sqlCmd.CommandText = sb.ToString()

  Using DataReader As SqlDataReader = _sqlCmd.ExecuteReader()
      Do While DataReader.Read()
         ... fill the list with objects ...
      Loop
  End Using

  Return result
End Function

我的日志是干净的表单错误。那么在一秒钟内打开与服务器的连接是否有问题，就像我使用它一样？

编辑：

我现在已经做了很多测试来确定问题。我发现只是多次连接到服务器不会导致任何问题。连接后也没有添加select语句。但是当我实际实现一个函数时，完整的阅读器部分并返回我的结果，我会遇到超时问题。这是两个例子。

这不会导致问题：

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs)
    Me.DataContext = Me
    m_Thread = New Thread(AddressOf ConnectionTestFunction)
    m_Thread.IsBackground = True
    m_Thread.Start()
End Sub

Private Sub ConnectionTestFunction()
    While m_stopThread = False
        Try
            m_log.WriteLine("GetData (" & m_ThreadCounter & ")")
            Using cnn As SqlConnection = New SqlConnection("Data Source=server;Initial Catalog=db;Integrated Security=True;MultipleActiveResultSets=True")
                cnn.Open()
                Using cmd As SqlCommand = New SqlCommand("SELECT * FROM Data", cnn)
                    Using DataReader As SqlDataReader = cmd.ExecuteReader()
                        Do While DataReader.Read()
                        Loop
                    End Using
                End Using
            End Using
        Catch ex As Exception
            m_log.WriteLine(ex.ToString())
        End Try
        m_ThreadCounter += 1
        Thread.Sleep(1000)
    End While
End Sub

这会导致超时错误：

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs)
    Me.DataContext = Me
    m_Thread = New Thread(AddressOf ConnectionTestFunction)
    m_Thread.IsBackground = True
    m_Thread.Start()
End Sub

Private Sub ConnectionTestFunction()
    While m_stopThread = False
        Try
            m_log.WriteLine("GetData (" & m_ThreadCounter & ")")
            Dim datarows As List(Of Data) = Me.GetData()
        Catch ex As Exception
            m_log.WriteLine(ex.ToString())
        End Try
        m_ThreadCounter += 1
        Thread.Sleep(1000)
    End While
End Sub

Private Function GetData() As List(Of Data)
    Dim result As New List(Of Data)
    Using cnn As SqlConnection = New SqlConnection("Data Source=server;Initial Catalog=db;Integrated Security=True;MultipleActiveResultSets=True")
        cnn.Open()
        Using cmd As SqlCommand = New SqlCommand("SELECT * FROM Data", cnn)
            Using DataReader As SqlDataReader = cmd.ExecuteReader()
                Do While DataReader.Read()
                    Dim d As New Data()
                    d.DataId = DataReader("DataId")
                    ... etc fields about 10 of them ...
                    result.Add(d)
                Loop
            End Using
        End Using
    End Using
    Return result
End Function

如果有人对此有任何想法，我真的很高兴......我不得不承认我现在真的很困惑。

Answer 1

您的代码可能需要比连接的默认超时值更长的时间才能完成。尝试在创建Sql连接时指定超时。确保它比代码完成所需的时间更长。

Answer 2

这种方法看起来不是很好..为什么不在新数据到来时做出反应？您可以使用触发器或SqlDependency？

http://dotnet.dzone.com/articles/c-sqldependency-monitoring

vb.net每秒轮询一次Sql server导致超时

2 个答案: