The real answer is twofold: 1. Lots of batch jobs. Sometimes it's unclear how much value they produce / whether they're still used. 2. Twitter probably made a

The real answer is twofold: 1. Lots of batch jobs. Sometimes it's unclear how much value they produce / whether they're still used. 2. Twitter probably made a mistake early on in taking a fanout-on-write approach to populate feeds. This is super expensive and necessitates a lot of additional infrastructure. There is a good video about it here: https://www.youtube.com/watch?v=WEgCjwyXvwc https://www.youtube.com/watch?v=WEgCjwyXvwc