Question

我创建了这个函数，以递归方式从FTP服务器复制整个目录。它工作得很好，除了它比使用FileZilla执行相同操作慢大约4倍。在FileZilla中下载目录大约需要55秒，但使用此功能需要229秒。我该怎么做才能让它下载/运行得更快？

Private Sub CopyEntireDirectory(ByVal directory As String)
    Dim localPath = localDirectory & formatPath(directory)
    'creates directory in destination path
    IO.Directory.CreateDirectory(localPath)

    'Gets the directory details so I can separate folders from files
    Dim fileList As ArrayList = Ftp.ListDirectoryDetails(directory, "")

    For Each item In fileList
        'checks if it's a folder or file: d=folder
        If (item.ToString().StartsWith("d")) Then
            'gets the directory from the details
            Dim subDirectory As String = item.ToString().Substring(item.ToString().LastIndexOf(" ") + 1)
            CopyEntireDirectory(directory & "/" & subDirectory)
        Else
            Dim remoteFilePath As String = directory & "/" & item.ToString().Substring(item.ToString().LastIndexOf(" ") + 1)
            Dim destinationPath = localPath & "\" & item.ToString().Substring(item.ToString().LastIndexOf(" ") + 1)
            'downloads file to destination directory
            Ftp.DownLoadFile(remoteFilePath, destinationPath)
        End If
    Next
End Sub

以下是一直在占用的下载功能。

Public Sub DownLoadFile(ByVal fromFilename As String, ByVal toFilename As String)
    Dim files As ArrayList = Me.ListDirectory(fromFilename, "")
    Dim request As FtpWebRequest = Me.CreateRequestObject(fromFilename)
    request.Method = WebRequestMethods.Ftp.DownloadFile

    Dim response As FtpWebResponse = CType(request.GetResponse(), FtpWebResponse)
    If response.StatusCode <> FtpStatusCode.OpeningData AndAlso response.StatusCode <> FtpStatusCode.DataAlreadyOpen Then
        Throw New ApplicationException(Me.BuildCustomFtpErrorMessage(request, response))
    End If

    Dim fromFilenameStream As Stream = response.GetResponseStream()
    Dim toFilenameStream As FileStream = File.Create(toFilename)

    Dim buffer(BLOCK_SIZE) As Byte
    Dim bytesRead As Integer = fromFilenameStream.Read(buffer, 0, buffer.Length)
    Do While bytesRead > 0
        toFilenameStream.Write(buffer, 0, bytesRead)
        Array.Clear(buffer, 0, buffer.Length)
        bytesRead = fromFilenameStream.Read(buffer, 0, buffer.Length)
    Loop

    response.Close()
    fromFilenameStream.Close()
    toFilenameStream.Close()
End Sub

Answer 1

显然，慢速将在FTP命令中。递归地运行其他代码可能每秒运行一百万次，因为它没有任何内容。

FTP下载（无论它是什么）应该能够定义块的大小是grabs。这将是您速度的关键。它需要根据您的连接速度和文件大小进行优化。每个人都没有正确的号码。

修改

基于新代码，问题出在BLOCK_SIZE中，我认为这是一个常量。玩这个大小来获得最佳速度。

提示：这应该是1024的倍数

如何使这个递归函数更有效？

1 个答案: