That explains how you serve the same data to that user, but the more interesting problem is: how do you propagate the changes to the rest of the users over time?
Do you run some sort of backlog daemon that moves stuff between the different shards? And how is that faster than doing so immediately (the same data would be moved either way...)?
Do you run some sort of backlog daemon that moves stuff between the different shards? And how is that faster than doing so immediately (the same data would be moved either way...)?