Question

我正在执行一个简单的练习，即打开SQL Server数据库连接，从DataReader对象中提取表的第一条记录，然后关闭该对象。但是，我注意到在关闭连接时有大约5秒左右的延迟。但是，延迟仅在命令对象执行指定查询后发生。我曾经在这样的设置中工作，并且不记得关闭连接时有这么长的延迟。

   Public Sub TestDb()
    Dim cnStrBuilder As New SqlClient.SqlConnectionStringBuilder
    Dim cn As New SqlClient.SqlConnection
    Dim sqlSelectName As New SqlClient.SqlCommand
    Dim drName As SqlClient.SqlDataReader
    Dim newName As New SymName
    Dim i As Integer

    cnStrBuilder.UserID = "sa"
    cnStrBuilder.ConnectTimeout = 30
    cnStrBuilder.Password = ""
    cnStrBuilder.PersistSecurityInfo = True
    cnStrBuilder.DataSource = "EMARKET\FL_DB"
    cnStrBuilder.InitialCatalog = "EmailMarketing"

    sqlSelectName.CommandType = CommandType.Text
    sqlSelectName.CommandText = "SELECT * FROM [NAME]"

    System.Console.WriteLine(cnStrBuilder.ConnectionString)

    cn.ConnectionString = cnStrBuilder.ConnectionString

    Try
        If cn.State = ConnectionState.Closed Then
            cn.Open()
        End If
        System.Console.WriteLine("Connection success")

        sqlSelectName.Connection = cn

        System.Console.WriteLine("Execute Reader")
        drName = sqlSelectName.ExecuteReader

        If drName.HasRows = True Then
            System.Console.WriteLine("Read Row")
            drName.Read()

            For i = 0 To drName.FieldCount - 1
                Console.WriteLine(drName.Item(i).ToString)
            Next
        End If

        System.Console.WriteLine("Closing connection")

        sqlSelectName.Connection.Close()

    Catch ex As Exception
        System.Console.WriteLine("Something Happened")
        System.Console.WriteLine(ex.Message)
    End Try

System.Console.WriteLine("Done.")

End Sub

如果我省略了行

'System.Console.WriteLine("Execute Reader")
'drName = sqlSelectName.ExecuteReader
'
'If drName.HasRows = True Then
'    System.Console.WriteLine("Read Row")
'    drName.Read()
'
'    For i = 0 To drName.FieldCount - 1
'        Console.WriteLine(drName.Item(i).ToString)
'    Next
'End If

连接几乎立即关闭。是什么赋予了？我已将其缩小到导致连接延迟的.ExecuteReader行关闭的位置。 导致延迟的原因是什么？如何解决？

Answer 1

您告诉SQL Server检索整个表。然而，在第一行之后，您停止并关闭连接。和你一样，我希望连接能够立即关闭，但也许服务器正在忙着将表格转移到可以快速返回数据的地方。

如果您只询问服务器一行，连接是否仍然缓慢关闭？ F.e。

 sqlSelectName.CommandText = "SELECT TOP 1 * FROM [NAME]"

Answer 2

通常，您应该在使用包含连接对象的语句中包装任何实现IDisposable的对象。我会尝试实现以下来自MSDN的内容：

http://msdn.microsoft.com/en-us/library/y6wy5a0f.aspx#Y400

Public Sub CreateCommand(ByVal queryString As String, _
  ByVal connectionString As String)
    Using connection As New SqlConnection(connectionString)
        Dim command As New SqlCommand(queryString, connection)
        connection.Open()
        Dim reader As SqlDataReader = _
            command.ExecuteReader(CommandBehavior.CloseConnection)
        While reader.Read()
            Console.WriteLine("{0}", reader(0))
        End While
    End Using
End Sub

试图关闭ADO.NET连接对象的异常长暂停：这是正常的吗？

2 个答案: