How HTTP/2 pushes the web: An empirical study of HTTP/2 server push

The simplicity of HTTP made it the default building block for desktop and mobile apps, yet it suffers from inherent inefficiencies in the modern web. HTTP/2 was designed to address these inefficiencies and its adoption remarks a major protocol shift in the Internet. Despite this relevance, its Internet-wide adoption remains unknown. Especially, the adoption and use of server push - advertised as a key feature to further reduce page load times - is completely unexplored. To answer both questions, we provide large-scale measurements of the HTTP/2 adoption and usage of server push in the wild, probing the entire IPv4 address space and the complete set of .com/.net/.org domains. We find 5.38M HTTP/2 enabled domains hosted by only few infrastructures driving this adoption. While we find the overall HTTP/2 adoption to increase, only few hundred domains utilize server push. We examine pushed content, push strategies and identify the use of currently undocumented push strategies. Moreover, we discover large sources of overheads through server push for reoccurring page visits. By measuring page load times, we show that while push can speed up webpages, it also can slow them down - motivating the need for optimized push strategies.