[Twisted-Python] Nagle delays and twisted

Jp Calderone exarkun at divmod.com
Tue Aug 30 14:31:54 EDT 2005

On Tue, 30 Aug 2005 11:18:22 -0700, Brian Granger <bgranger at scu.edu> wrote:
>Hello all,
>I have been implementing a custom protocol with twisted and have been 
>having some odd performance problems.  My protocol consists of a TCP 
>connection with multiple client/server commands.  For some types of 
>commands, I found it took about 200 ms for the client and server to 
>complete.  Because this was over loopback (which has a ping of 0.1  ms), it 
>seems very slow.  Because I am keeping the socket connected,  I am not 
>measuring the socket setup time.  Lucky for me, there was a  discussion 
>about this issue on comp.lang.python recently:
>I guess the 200 ms delay is a well known effect of the Nagle  Algorithm that 
>TCP uses.  Supposedly, this delay can be eliminated by  i) setting 
>TCP_NODELAY on the socket or ii) avoiding sending multiple  small messages 
>without a response from the other end.
>My understanding is that protocols that do the following will run  into the 
>C: short message 1
>C: short message 2
>S: reply for message 1 and 2
>What is the preferred way of setting TCP_NODELAY on a socket  controlled by 
>twisted?  Are there any adverse side effects that this  will have?

In your protocol's connectionMade (or at any other time you desire):


Passing False will re-enable nagling.  The problems this can cause are primarily an increase in bandwidth usage (and thus increased latency if a link carrying the traffic is near or at saturation) if the change results in segments which would have been combined to be sent separately.


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