Sharding and HTTP/2 Connection Reuse Revisited: Why Are There Still Redundant Connections?

10/27/2021

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by   Constantin Sander, et al.

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HTTP/2 and HTTP/3 avoid concurrent connections but instead multiplex requests over a single connection. Besides enabling new features, this reduces overhead and enables fair bandwidth sharing. Redundant connections should hence be a story of the past with HTTP/2. However, they still exist, potentially hindering innovation and performance. Thus, we measure their spread and analyze their causes in this paper. We find that 36 of the Alexa Top 100k websites cause Chromium-based webbrowsers to open superfluous connections. We mainly attribute these to domain sharding, despite HTTP/2 efforts to revert it, and DNS load balancing, but also the Fetch Standard.