Tens of thousands across
all the organizations where postgres and clickhouse are used, maybe (though even then probably not!).
Not tens of thousands at any one organization supporting postgres and clickhouse.
No single organization needs even hundreds of people to support these apps. You just need a good architecture and a handful of dba's, developers, and sysadmins... maybe.. depending on your scale. At many smaller orgs you can probably get away with one.
