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:
http://groups.google.com/group/comp.lang.python/browse_frm/thread/ 507a711c61df7ad5/d6e871a24d8506a6#d6e871a24d8506a6
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 problem:
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?
And second: does anyone have any tips for designing protocols that avoid this delay without setting TCP_NODELAY? The obvious solution is to have a reply for each message:
C: short message 1 S: reply for 1 C: short message 2 S: reply for 2
But... this increases the latency of the protocol. Any ideas or experiences with these issues would be greatly appreciated.
Thanks
Brian