我被要求做一个系统，该系统每秒轮询数据库中的一个表，如果它对符合条件的行进行计数，则开始操作来处理它。
我已经这样做了，但时不时地我得到一个超时异常。我有一个 WPF 应用程序，其中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。
下面是我的线程子：
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
现在我的日志似乎随机出现超时异常：
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：这完全可以节省吗？还是我在这里做一些根本错误的事情？当然，如果有人有解决此问题的建议。
编辑：
我用 SQL 函数尝试了一些不同的方法。当我的应用程序启动并转储“使用”子句时，我现在打开一个连接。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。那么像我使用使用一样，每秒打开一次到服务器的连接有什么问题吗？
编辑：
我现在已经做了很多测试来确定问题所在。我发现只是多次连接到服务器不会导致任何问题。在连接后添加 select 语句也不行。但是当我实际实现一个完整的阅读器部分并返回我的结果时，我遇到了超时问题。这里有两个例子。
这不会引起问题：
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。