Well, that doesn't really help very much. Even if it's not "a lot", different people define "a lot" rather differently, so again, we still have no idea what constraints exist in your environment, nor even the slightest clue as to how much data we're talking about. Without concrete details, anything anyone provides is, at best, guesswork. All we know so far is that you have some legacy data that needs to make it into production tables without any "down time". We don't even have any definition as to exactly what "down time" means. In some places, that phrase could even apply to degradation of production response times due to an unforeseen additional load, however slight. For others, down time is only when the entire application is unavailable. Given that the term "production" could refer to anything from just one application to an entire fleet of apps, that too starts to lose meaning. There are way too many variables here to be able to offer much in the way of detailed advice. Do you even have any ideas on how you plan to do this without down time? You'll need to provide a heck of a lot more detail before useful advice is likely to be forthcoming.