Netflix documentary The Playlist about Spotify, they present one of the technical breakthroughs that they created their own TCP implementation to reduce the latency from first click to playing the song to less than 250ms.
I don't find any resources on the Internet explaining what they did, but I found this presentation that probably describes this: https://www.csc.kth.se/~gkreitz/spotify/kreitz-spotify_kth11.pdf
Slide 21/22
But what does "Configure kernels to not follow the RFC 5681 SHOULD." actually mean?