I'd be interested in seeing why instagram didn't implement the suggested user service as a batch process that populated some KV store. Online evaluation is great for guaranteeing up-to-date results, but the tradeoff is that you now have to bring up and maintain a fairly critical production service.

> The SU service fetches candidate accounts from various sources, such as your friends, accounts that you may be interested in, and popular accounts in your area. Then, a machine learning model blends them to produce a list of personalized account suggestions.

> This enabled us to reduce the number of instances of the Suggested Users service from 720 to 38.