Bearing in mind that primary key, and clustered key are not necessarily the same thing, your point stands that the uuid does not need to be the clustered key.
Renumbering bigint primary keys, so as the effect a one-time merge, becomes substantially less trivial if the desire for minimal downtime, coupled with hundreds of related tables, and tens of sites are in play.
Renumbering bigint primary keys, so as the effect a one-time merge, becomes substantially less trivial if the desire for minimal downtime, coupled with hundreds of related tables, and tens of sites are in play.