sftp performance problem, cured by TCP_NODELAY

Chris Rapier rapier at psc.edu
Fri Jan 27 05:47:05 EST 2006

Miklos Szeredi wrote:
>> Better logic to control NODELAY usage makes sense. I never looked 
>> closely at this portion of the code but perhaps it could be triggered by 
>> a request for remote TTY.
> That is what the current code does.  And that is the source of the
> bug, since NODELAY is needed for some non-interactive traffic, like
> sftp.

I'm sorry. I must have read the previous messages wrong. I was under the 
impression that Nagle was being disabled for interactive sessions. Which 
is silly.

>> I actually agree with Damien on this point. There shouldn't be a user 
>> setting. The software should be able to determine when NODELAY should 
>> and shouldn't be set. While it might be more difficult to create a 
>> generalized solution because of port fowarding issue a more specific 
>> solution that will capture 95% of the common usage situations should be 
>> feasible.
> Well, currently the software is doing the wrong decision, and I'm not
> entirely convinced, that there is any other valid heuristic than to
> turn NODELAY on unconditionally.

hurm... because the ssh code is basically unaware of what the client, in 
this case sftp, is actually doing, right? So unless a switch is passed 
you can't identify the specific needs of the client?

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