Using HTTP/1 (GODEBUG=http2client=0), calling this function 100 times against index.golang.org takes ~710 milliseconds on Go 1.26 on my machine. On Go 1.27, the same program takes ~150 milliseconds.
That is almost 5 times faster! How is such a drastic performance difference possible?
To understand the difference, consider what happens on the network when we make an HTTP request.
These round trips (plus some CPU time spent on TLS handshakes) add up quickly. In cross-region communications, one-way latencies often reach or exceed the 50 ms (100 ms RTT) shown in the diagram above. Compared to the 300 ms spent just setting up the connection, the HTTP request itself can be cheap to serve, taking only a little over 1 RTT when bandwidth is plentiful or the HTTP response is small.
