sftp performance problem, cured by TCP_NODELAY

[Miklos Szeredi]

> > I really can't imagine Nagle helping all that much, when it's already
> > disabled (without people noticing) for the most important case of
> > interactive traffic.
> 
> I actually forgot about something which leads me to believe that
> disabling Nagle in all cases is appropriate appropriate at this
> time.  Delayed ACK. Bad interactions. Also, I forgot, if you ever
> end up using multiple channels in SSH (it is multiplexed after all)
> I think you can only use Nagle on a per connection (not per channel)
> basis. That is what SFTP is doing isn't it? A data channel and
> control channel in the same connection?

Yes.

> It would be nice to get a better mechanism in place because not
> having Nagle is inherently limiting. Being that ssh is multiplexed
> anyway you could probably just re-implement something like it on a
> per channel basis.

Ssh doesn't see it as two separate channels, just a single
bidirectional stream.

Also I'm not sure if it's possible to implement Nagle in the
application layer, without knowledge of network congestion state.

Miklos