keep-alive slowdown caused by Nagle's Algorithm

[dalke]

When I use this test program

from paste import httpserver def echo_app(environ, start_response):

n = 10000 start_response("200 Ok", [("Content-Type", "text/plain"),

("Content-Length", str(n))])

return ["*" * n]

httpserver.serve(echo_app, protocol_version="HTTP/1.1")

I get about 1,300 request per second with

httperf --server localhost --port 8080 --num-conn 100

but only about 11 request per second with

httperf --server localhost --port 8080 --num-calls 100

There should be no reason for keep-alive to have such a bad performance.

I tracked it down to the outgoing/response in the server. The server wrote the text to the socket but the OS in the TCP layer buffered the text for up to 0.2s hoping to combine multiple packets into one. But the client is just waiting, so eventually the timeout kicks in. But 5 timeouts for out of 11 (on average) gives a performance of about 11 responses per second.

I've attached a fix, which does

self.socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)

[dalke]

patch to httpserver.py

[dalke]

More details are on the paste list at

 http://groups.google.com/group/paste-users/browse_thread/thread/b2afc88a86caade1

and on StackOverflow? at

 http://stackoverflow.com/questions/1781766/paste-httpserver-and-slowdown-with-http-1-1-keep-alive-tested-with-httperf-and-a