Yea, the Monolith paper by Bytedance uses Flink but they only say it's in use for their B2B ecommerce optimization system. Maybe this is intentional ambiguity, but I'd believe that they wouldn't rely on something like Flink for their core TikTok infrastructure.

My hunch is we start to learn a lot more about the core internals as Oracle tries to market to B2B customers, as Oracle is wont to do!

Flink is not really a performance choice, it's bloat to throw software as fast as possible at problems. I don't think there's any benchmark demonstrating insane capabilities per machine. I definitely couldn't get it to any numbers I liked, given other stream processing / state processing engines that exist (if compute and inmemory state management is the goal). Pretty sure any pathway that touches RocksDB slows everything down to 1-10k events per second, if not less.

The problem of finding out which video is next, by immediately taking into account the recent user context (and other user context) is completely unrelated to what Flink does -- exactly-once state consistency, distributed checkpoints, recovery, event-time semantics, large keyed state. I would even say you don't want a solution to any of the problems Flink solves, you want to avoid having these problems.