The SFTP Flow Control Should be Autotuning by Default

[rapier1]

` -X sftp_option
Specify an option that controls aspects of SFTP protocol behaviour. The valid options are:

         nrequests=value
                 Controls how many concurrent SFTP read or write requests may be in progress at any point in time during a download or upload.  This value must be between 1 and 8192.
                 By default 1024 requests may be active concurrently.

         buffer=value
                 Controls the maximum buffer size for a single SFTP read/write operation used during download or upload. This value must be between 1B and 255KB. You may use the K unit
                 for the size. E.g. 32768 or 32K.  By default a 32KB buffer is used.`

This is also a new option in scp as well in order to pass those parameters to sftp. The default works out to be 32MB but honestly, that’s a trap because people don’t think about doing that. It would be better if the nrequest value could vary over the life of the connection in response to the current buffer size from ssh. eg ssh_bufsize / sftp_buffer_size = nrequests