Facebook Interview Question for Software Engineer / Developers


Country: United States
Interview Type: In-Person




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- Earlier users had to buy credits per application but now with virtual currency, user can use the same credit in any Facebook affiliated application.
- Single user's credit balance is more of a user specific information now as compared to user's account info for a specific application. Therefore it can be combined with existing user info.
- Our aim is to atomically and securely purchase and spend virtual currency thereby updating user's current balance.
- @fb user info is cached with memcached which provides us with performance in fetching user data, replication for availability, atomic transactions using 2-phase commit, fault tolerance, cache coherency etc.
- For each expenditure we check user balance, if more or equal to be spent balance calculated accordingly and saved.

I'm really not sure, what exactly do they expect here. If they're ok with us leveraging their architecture then we don't have much to say here but if they want us to design everything from scratch then probably we need to explain memcached and DHT here.

- Second Attempt November 19, 2012 | Flag Reply


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