We were replacing a fully SQL email engine (that was starting to fall over due to load) with this more hybrid approach; we had customers, we knew that the busin

We were replacing a fully SQL email engine (that was starting to fall over due to load) with this more hybrid approach; we had customers, we knew that the business case closed, but the load was starting to overpower the main database, so we spun off separate databases, and bought ourselves a little more overhead by splitting out the normalized and denormalized data. Could well have been a mistake, but we weren't thrilled with postgres ability to scale horizontally, so went to CB so we could scale a bit more. (As I recall, we were doing 7m emails a day, our goal was to support up to 70m with that structure.)