Yes, the explanation given does not seem to pass the sniff test. If all the wall-time is being taken in recv(), there's no reason why using epoll() would be any improvement.
The reason the python version is slow is (I believe) that the code is very inefficient. It uses socket.sendall() instead of sockfile.write/flush. Using sockfile.write/flush speeds it up from 50 requests/second to 7k requests/second on my machine.
I'm the author of the original post. The difference has nothing to do with epoll, these comments are correct. Thanks particularly to codeape for his pull request which made me realise this. Sorry everyone. I will fix the post.
Reducing the number of send calls, in both the C and Python versions, makes them enormously faster. Go is already batching up the writes, hence the apparent speed advantage.
If you strace the client, you see that the "get" case was replying with two send calls, one for the "VALUE" line, another with the value and "END". All the time is consumed with the client waiting to receive that second message. Depending on the client, and I tried a bunch of ways, it's either in 'poll' (pylibmc), 'futex' (Go), or 'recv' (basic python socket). That second receive is about two orders of magnitude slower than the previous recv.
Why does reading that second line take so much longer?
Yes, thank you! Adding this line to the two-writes Python version (memg-slow.py on github) makes it about as fast as the single write version (memg.py on github):
