Re: Sftp: performance enhancing changes

[Joseph Galbraith <galb%vandyke.com@localhost>]

Peter Gutmann wrote:
> Joseph Galbraith <galb%vandyke.com@localhost> writes:
>>o Ignoring channel window makes for a screaming
>> sftp transfer. (unacceptable, breaks multiplexing.)
>
> It's only unacceptable if you're actually doing multiplexing.  If you're just
> using SFTP as a secure FTP replacement (which is what many people seem to be
> using it for), it's a simple, quick fix for the SFTP performance problems.

It is unacceptable because draft-ietf-secsh-connect-17
states in section 3.2:

> The maximum amount of data allowed is the current window size.
> The window size is decremented by the amount of data sent.  Both
> parties MAY ignore all extra data sent after the allowed window is
> empty.

And our server _will_ drop data that
exceeds the channel window.

The sftp draft can't override this rule, and I
don't think we are going to change the connection
draft.

(To be honest I don't think we should either.)

Sorry, I should have been clearer on why
I thought it was unacceptable.

In addition, proper management of packet size and
channel windows can mean that there is no or very
little overhead from obeying the rules.

- Joseph