After upgrade to HTTP/2 websites may appear slower even though they are faster…
- On a normal (slow) website, maybe the page takes 5 seconds to completely finish loading, but you didn’t notice because all the visible part of the page loaded in 2 seconds.
- After upgrade to HTTP/2, maybe the page takes 4 seconds to load. Now, even though it is faster, one of the images at the top of the screen only appears after 4 seconds. So the now from visitor point of view it looks like the page takes 4 seconds to load instead of 2.
So what happens on a slow/unstable internet connection? (Yes, a lot of people still have these).
- on the one hand there is a massive [but largely invisible] latency improvement thanks to HTTP/2 reducing the number of requests going over the network
- on the other hand, the images are normally way over 50% of the bandwidth, so as the bandwidth goes down, the impact of any change to image load sequence goes up. If the load sequence changes the images at the top of the screen could be seriously delayed.
So, with HTTP/2 web optimization is still highly advisable, especially image compression, and avoiding really long pages with hundreds of images that are not going to be in the visible area of the screen…
Title pic from great article here: https://99designs.co.uk/tech-blog/blog/2016/07/14/real-world-http-2-400gb-of-images-per-day/