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Rebex FTP/SSL
.NET FTP client
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.NET SSH Shell
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All Rebex .NET libraries together
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Transfer speed management
On this page:
Limiting transfer speed (bandwidth throttling)
High transfer speed is not always desirable - if you prefer high network throughput, you might wish to limit the transfer speed.
To achieve this, use MaxDownloadSpeed
and MaxUploadSpeed
properties:
// set download and upload speed limits sftp.MaxDownloadSpeed = 4 * 1024; sftp.MaxUploadSpeed = 2 * 1024; // transfer files // ...
' set download and upload speed limits sftp.MaxDownloadSpeed = 4 * 1024 sftp.MaxUploadSpeed = 2 * 1024 ' transfer files ' ...
Speed monitoring (transfer speed event)
To keep informed about the current speed of the transfer (in order to display it to the user, for example),
register a TransferProgressChanged
event handler. Current transfer speed is available through
SftpTransferProgressChangedEventArgs.BytesPerSecond
property,
moving average calculation is used to smooth the value.
Sample event handler:
void client_SpeedMonitoring(object sender, SftpTransferProgressChangedEventArgs e) { // display current speed info Console.WriteLine("Current speed: {0} B/s", e.BytesPerSecond); }
Sub client_SpeedMonitoring(ByVal sender As Object, ByVal e As SftpTransferProgressChangedEventArgs) ' display current speed info Console.WriteLine("Current speed: {0} B/s", e.BytesPerSecond) End Sub
Registering the event handler:
// register TransferProgressChanged event handler sftp.TransferProgressChanged += client_SpeedMonitoring; // transfer files // ...
' register TransferProgressChanged event handler AddHandler sftp.TransferProgressChanged, AddressOf client_SpeedMonitoring ' transfer files ' ...
Optimized transfer (request queuing)
In SFTP protocol, files are transferred in blocks of several kilobytes each. For each block, the client needs to send a request and receive a response.
This is how a simple transfer might look like at the protocol level:
Client request 1: Read 10000 bytes at position 0.
Server response 1: Success. Data: [data blob]
Client request 2: Read 10000 block at position 10000.
Server response 2: Success. Data: [data blob]
Client request 3: Read 10000 block at position 20000.
Server response 3: Success. Data: [data blob]
Client request 4: Read 10000 block at position 30000.
Server response 4: Success. Data: [data blob]
...
However, this simple approach would result in suboptimal transfer speed on high-latency networks because the server has nothing to do while waiting for each subsequent request.
To achieve higher throughput, Rebex SFTP uses a more advanced approach - request queueing:
Client request 1: Read 10000 bytes at position 0.
Client request 2: Read 10000 block at position 10000.
Client request 3: Read 10000 block at position 20000.
Server response 1: Success. Data: [data blob]
Client request 4: Read 10000 block at position 30000.
Server response 2: Success. Data: [data blob]
Client request 5: Read 10000 block at position 40000.
Server response 3: Success. Data: [data blob]
Client request 6: Read 10000 block at position 50000.
Server response 4: Success. Data: [data blob]
...
This eliminates the delay at the server - it no longer has to wait for subsequent requests because
they are already in its request queue.
All properly implemented SFTP servers should support this approach and it is enabled by default.
To switch it off (not recommended), set Sftp.Settings.DisableTransferQueue
to true
.
Tip: To tweak transfer queue lengths and buffer sizes, use
Sftp.Settings.DownloadQueueLength
/Sftp.Settings.UploadQueueLength
and
Sftp.Settings.DownloadBufferSize
/Sftp.Settings.UploadBufferSize
properties.
Large buffer mode
Occasionally, using larger buffers may increase the transfer speed, particularly for downloads.
Set Sftp.Settings.UseLargeBuffers
to true
to use larger buffers.
Internal buffer sizes:
Buffer | No option | UseLargeBuffers |
---|---|---|
TCP socket's receive buffer | Socket's default | 4MB |
TCP socket's send buffer | Socket's default | 256KB |
SSH channel's receive buffer | 128KB | 2MB |
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