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.
We've seen huge gains from making the system as realtime as possible. Consider a new user who hasn't followed anyone yet--each new follow is super helpful in informing the recommendation system.
> 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.