sftp performance problem, cured by TCP_NODELAY

Rick Jones rick.jones2 at hp.com
Fri Jan 27 09:14:29 EST 2006

Miklos Szeredi wrote:
>>>Done.  Can I now have my NODELAY please ;)
>>Got a syscall and packet trace showing "the right thing" being done?-)
> Can send it tomorrow.  But the best indication that it's right is that
> the performance problem is gone.

Ah then you misunderstood what I was getting at, sorry. Although seeing the 
traces with TCP_NODELAY set would be interesting, I meant traces showing sftp 
behaving properly and still getting hit with delays attributable to the Nagle 

> I don't know how far 4.3 is in the freeze state, but unconditionally
> setting NODELAY seems quite safe.  It is bound to drastically improve
> performance for many people, while any noticable performance
> regression is highly unlikely.  But anyway I leave that to you guys to
> decide.

HP-UX in 11.X decided to unconditionally disable Nagle in their telnetd.  They 
then discovered a whole slew of folks with "slow" clients that were then getting 
swamped by the thousands of tiny packets per second from a screen dump...they 
started dropping packets and thngs were worse than before. So I'd say that I do 
not agree with your assesment that noticable performance regression is highly 

rick jones
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