mysql - 数据读取过程中遇到 fatal error

Question

我正在进行定期更新表扫描

Using connect1 As New MySqlConnection(ConnectLocalhost.serverString)
    connect1.Open()
    Dim cmd = New MySqlCommand("set net_write_timeout=99999; set net_read_timeout=99999", connect1) ' // Setting tiimeout on mysqlServer
    cmd.ExecuteNonQuery()

    Dim BusinessReader = selectSomeQuery("Select * from tablebusiness limit 800,10000000", connect1)

    Do While BusinessReader.Read 'random exception here

有时我会收到此错误

MySql.Data.MySqlClient.MySqlException was unhandled
  ErrorCode=-2147467259
  Message=Fatal error encountered during data read.
  Number=0
  Source=MySql.Data
  StackTrace:
       at MySql.Data.MySqlClient.MySqlDataReader.Read()
       at dreamhost.Business.InsertLocalhost() in \\work\c\business\fromwork\currentprojects\program\library\vb.net\badger.vb:line 1849
       at dreamhost.Business.surFoursquare() in \\work\c\business\fromwork\currentprojects\program\library\vb.net\badger.vb:line 1939
       at dreamhost.traverseweb._Lambda$__92() in \\work\c\business\fromwork\currentprojects\program\library\vb.net\traverseweb.vb:line 77
       at dreamhost.buttonClicking.startAndStopClickingButton(Object sender, Action SomeSub) in \\work\c\business\fromwork\currentprojects\program\library\vb.net\buttonclicking.vb:line 45
       at dreamhost.traverseweb.foursquare_Click(Object sender, EventArgs e) in \\work\c\business\fromwork\currentprojects\program\library\vb.net\traverseweb.vb:line 77
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(ApplicationContext context)
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
       at dreamhost.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: MySql.Data.MySqlClient.MySqlException
       ErrorCode=-2147467259
       Message=Reading from the stream has failed.
       Number=0
       Source=MySql.Data
       StackTrace:
            at MySql.Data.MySqlClient.MySqlStream.LoadPacket()
            at MySql.Data.MySqlClient.MySqlStream.ReadPacket()
            at MySql.Data.MySqlClient.NativeDriver.FetchDataRow(Int32 statementId, Int32 columns)
            at MySql.Data.MySqlClient.Driver.FetchDataRow(Int32 statementId, Int32 columns)
            at MySql.Data.MySqlClient.ResultSet.GetNextRow()
            at MySql.Data.MySqlClient.ResultSet.NextRow(CommandBehavior behavior)
            at MySql.Data.MySqlClient.MySqlDataReader.Read()
       InnerException: System.IO.IOException
            Message=Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
            Source=MySql.Data
            StackTrace:
                 at MyNetworkStream.HandleOrRethrowException(Exception e)
                 at MyNetworkStream.Read(Byte[] buffer, Int32 offset, Int32 count)
                 at MySql.Data.MySqlClient.TimedStream.Read(Byte[] buffer, Int32 offset, Int32 count)
                 at System.IO.BufferedStream.Read(Byte[] array, Int32 offset, Int32 count)
                 at MySql.Data.MySqlClient.MySqlStream.ReadFully(Stream stream, Byte[] buffer, Int32 offset, Int32 count)
                 at MySql.Data.MySqlClient.MySqlStream.LoadPacket()
            InnerException: System.Net.Sockets.SocketException
                 ErrorCode=10054
                 Message=An existing connection was forcibly closed by the remote host
                 NativeErrorCode=10054
                 Source=System
                 StackTrace:
                      at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
                      at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
                 InnerException: 

我想要的只是让程序在这种情况发生时“继续”。但这似乎是不可能的。所以我想我需要一种方法来确保这个错误不会发生。它随机发生在大约 800 个条目左右。

在我看来，连接被远程主机强制关闭。在这种情况下，我只想回到原来的状态并重新开始。

Answer 1

连接断开的原因可能有很多(服务器负载、网络问题等)。您的程序崩溃表明您的数据库代码不受 try 语句的保护。如果你做这样的事情:

try
    Using connect1 As New MySqlConnection(ConnectLocalhost.serverString)
        connect1.Open()
        Dim cmd = New MySqlCommand("set net_write_timeout=99999;  _
          set net_read_timeout=99999", connect1) 
        cmd.ExecuteNonQuery()

        Dim BusinessReader = selectSomeQuery("Select *...", connect1)

        Do While BusinessReader.Read 
            'random exception here'
            '...more code'
        Loop
    End Using
Catch ex As Exception
    ' code breaks here on exception - recover from this point '
End Try

我不会写一篇关于异常处理的冗长论文，但如果你看一下的话，那里有很多资源。如何处理它取决于您的具体情况 - 是否记录异常、记录上次成功的操作是什么、是否尝试从原来的位置恢复或是否尝试重新执行整个操作、通知用户等

MSDN - Try/Catch/Finally