[methehack]

I think the regional keyspaces would be have to be caches -- denormalize it, basically. Pop/re-fresh people into the geo-based caches as they moved around. Truth sits behind it, centralized (perhaps partitioned in some way that makes sense globally but is sub-optimal from a regional cache perspective). Might not be worth it -- hard to know from here. :)

[ajslater]

afaik, this is how Facebook does it, but with regional sources of truth. If you signed up for FB in Paris and move to San Francisco, your master profile lives in Europe in perpetuity and you'll use your regional cache forever in the USA. The number of people moving far away from their home DC's should be a reasonably small fraction of the total for it not to matter.