For a first guess, if there were 5 writing dbs, each could write every 5th id, starting at a different index (0,1,2,3,4). You'd end up with globally unique ids

For a first guess, if there were 5 writing dbs, each could write every 5th id, starting at a different index (0,1,2,3,4). You'd end up with globally unique ids, and as long as your writes were (approx.) evenly distributed, all 5 sequences would be (approx.) close to each other. Who knows, they might have 100 writable dbs, with only 70% up at any point in time, meaning only 70% of all integers are actually used.. anyway, I don't know, I can just imagine them doing something like this if they wanted certain things from the system.