sftp performance problem, cured by TCP_NODELAY

Rick Jones rick.jones2 at hp.com
Wed Jan 25 05:23:51 EST 2006

Miklos Szeredi wrote:
> In certain situations sftp download speed can be much less than that
> of scp.
> After many days of trying to find the cause finally I found it to be
> the tcp nagle algorithm, which if turned off with TCP_NODELAY
> eliminates the problem.
> Now I see it being discussed back in 2002, but it still unresolved in
> openssh-4.2 :(
> Simple solution would be to add a NoDelay option to ssh which sftp
> would set.  The proprietary ssh seems to already have this option.

What sort of socket calling pattern was sftp making that had it running into 
issues with Nagle and delayed ACK?

rick jones

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