Measuring HTTP/3: Adoption and Performance

The third version of the Hypertext Transfer Protocol (HTTP) is in its final standardization phase by the IETF. Besides better security and increased flexibility, it promises benefits in terms of performance. HTTP/3 adopts a more efficient header compression schema and replaces TCP with QUIC, a transport protocol carried over UDP, originally proposed by Google and currently under standardization too. Although HTTP/3 early implementations already exist and some websites announce its support, it has been subject to few studies. We provide a first measurement study on HTTP/3 adoption and performance. We testify how it has been adopted by some of the leading Internet companies such as Google, Facebook and Cloudflare in 2020. We run a large-scale measurement campaign towards thousands of websites adopting HTTP/3, aiming at understanding to what extent it achieves better performance than HTTP/2. We find that adopting websites often host most web page objects on third-party servers, which support only HTTP/2 or even HTTP/1.1. As excepted, websites loading objects from a limited set of third-party domains (avoiding legacy protocols) are those experiencing larger performance gains. Our experiments however show that HTTP/3 provides sizable benefits only in scenarios with high latency or poor bandwidth.