Instagram Architecture Update: What’s New With Instagram?
If read capacity is likely to be a concern, bringing up read-slaves ahead of time and getting them in rotation is ideal; if any new read issues crop up, however, know ahead of time what your options are for bringing more read capacity into rotation.
.. Know where to shed load if needed. Display shorter feeds, for example.
.. Instagram succeeded more on its understanding of the power of psychology in design than technology.
..I think that the user_id’s might be in stored redis, and memcache would have the entire user record + joined data from the primary data store.