[jessep]

Sort of related, but we had to shard as usage grew and didn’t have uuids and it was annoying. Wasn’t the most annoying bit though. Whole thing is pretty complex regardless of uuid, if you have a highly interconnected data model that needs to stay online while migrating.

[iainctduncan]

Right, but if you start off with uuids and the expectation that you might use them to shard, you'll wind up factoring that into the data model. Retrofitting, as you rightly say, can be much harder.