> In most databases, altering a schema is an operation that's over quickly
I think many people were burned by MySQL InnoDB, which modifies (or modified; I'm still on quite an old version) schemas by making a new table and copying the data, and don't realise that all databases don't do that.
InnoDB tables have online, non-copying (for most operations) DDL in 5.6. Also, TokuDB has had online, non-copying DDL (column add and drop, add index) since TokuDB 5.0.
I think many people were burned by MySQL InnoDB, which modifies (or modified; I'm still on quite an old version) schemas by making a new table and copying the data, and don't realise that all databases don't do that.