Why you should understand (a little) about TCP - Julia Evans

Why you should understand (a little) about TCP - Julia Evans:



"Delayed ACKs & TCP_NODELAY



Ruby's Net::HTTP splits POST requests across two TCP packets - one for the headers, and another for the body. curl, by contrast, combines the two if they'll fit in a single packet. To make things worse, Net::HTTP doesn't set TCP_NODELAY on the TCP socket it opens, so it waits for acknowledgement of the first packet before sending the second. This behaviour is a consequence of Nagle's algorithm. Moving to the other end of the connection, HAProxy has to choose how to acknowledge those two packets. In version 1.4.18 (the one we were using), it opted to use TCP delayed acknowledgement. Delayed acknowledgement interacts badly with Nagle's algorithm, and causes the request to pause until the server reaches its delayed acknowledgement timeout.."

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