to start, some background:
we cache your timeline because building it every time you wanted to see it would be Slow and we can't have that. this cache is just a big list of post IDs because we can fetch posts quickly, we just can't build the list quickly.
when you publish a post, we fire off a series of background jobs that insert that post into all your followers' cached timelines. previously we were doing this in order based on when someone followed you (so earlier followers would see your posts sooner). this was kind of dumb and led to there being a sizable disparity in when posts would be seen on high-follower accounts.
so we randomized it. when you publish a post, we grab a list of all your followers, shuffle it, and then start handing out the post in that new random order. this means users at the end of the list will, on average, see posts sooner. yes this means users who followed early will, on average, see posts later. this doesn't actually make any material difference until you hit around 3k followers though so don't worry about it.
enjoy your slightly sooner / later post viewing.
this is a change that occurred to me as an option in the shower. my initial message in the chat was "i don't know if we should do this, but i also can't think of a ton of reasons why we shouldn't do this, and it'll be like two lines of code max, so we may as well"
