As a developer I fully support the notion of splitting the tools out from the server engine, like things are today.
But, realistically, pg_upgrade's functionality would need to be integrated into the server itself if we're ever going to have zero-downtime upgrades, right?
I don't know how other RDBMSs handle this, if at all
Yeah, the comment I was responding to addressed two different kinds of migration—schema migration and version upgrades—and my comment really applies more to schema migration than version upgrades; more support for smoothing the latter in the engine makes sense.
But, realistically, pg_upgrade's functionality would need to be integrated into the server itself if we're ever going to have zero-downtime upgrades, right?
I don't know how other RDBMSs handle this, if at all