Ok I'm curious: since this strategy sacrifices consistency, has anyone thoughts about something that is not full fan-out on reads or on writes ?

Let's imagine something like this: instead of writing to every user's timeline, it is written once for each shard containing at least one follower. This caps the fan-out at write time to hundreds of shards. At read time, getting the content for a given users reads that hot slice and filters actual followers. It definitely has more load but

- the read is still colocated inside the shard, so latency remains low

- for mega-followers the page will not see older entries anyway

There are of course other considerations, but I'm curious about what the load for something like that would look like (and I don't have the data nor infrastructure to test it)