Re: Why SFTP performance sucks, and how to fix it

[Markus Friedl <markus%openbsd.org@localhost>]

On Fri, Jul 11, 2003 at 05:01:31AM +1200, Peter Gutmann wrote:
> Markus Friedl <markus%openbsd.org@localhost> writes:
> 
> >when multiplexing multiple ssh channels over one connection and one of the
> >consumers is very slow, then the tcp flow control will not help. AFAIK, this
> >is one of the reasons why there's an additional per-channel flowcontrol.
> 
> Ahh, that makes sense.  Thanks.  Still, it just shows that there are different
> situations where the Ack-based flow control is appropriate, since the converse
> says that when not muxing multiple channels, TCP flow control should do.
> Specifically, if I'm using SFTP as just a secure FTP (without anything fancy
> like SSH port forwarding, just a dumb copy), it's just an updated form of
> rcp/scp: Open a connection, blast data across as quickly as possible, close
> the connection, either with a successful close or an unsuccessful disconnect
> on error, just as rcp does.  All I want at that point is the fastest possible
> transfer, if there's a flow-control problem TCP flow control will handle it,
> and if there's a fatal error then all you can do is close the session, just
> like standard rcp.

But then all you need to do is to announce a big window size.

E.g. the client can announce big window sizes if no pty allocation
is involved.  Recent OpenSSH's do this.