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SOLUTION.md

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Solution - The Case of the 50ms request

A common problem that can occur while using TCP is a ~40ms latency problem caused by the combination of Nagle's algorithm and TCP delayed acknowledgment used by the Linux kernel.

Possible solutions

Disabling Nagle's algorithm

In nodejs you can disable Nagle's algorithm using the following command,

req.setNoDelay(true);

Disabling delayed ACKs

In the server.py you can see the socket option,

setsockopt(socket.IPPROTO_TCP, socket.TCP_QUICKACK, 0)

to disable delayed ACKs by setting this option to 1, but notice that this can be changed by the protocol level implementation (see man 7 tcp).

Not splitting the POST request

In slow.js one can notice that the following line,

req.flushHeaders();

this forces the headers of the POST request without the data and only after sending the data. Removing this line will make the request sent in one packet preventing this bug.