What's "this" in your question? I don't see the immediate connection between a programmer's workflow and a database row update. But your understanding of what

What's "this" in your question? I don't see the immediate connection between a programmer's workflow and a database row update. But your understanding of what happens inside the database engine is too simplistic: first of all, the data does not necessarily exist as only one copy because there may be multiple indexes or materialized views covering that data. And each copy needs its own pointer switch as the very last operation. Secondly, the "atomic" change you mention is only atomic from the application point of view. Multiple clients may each have their own isolation levels and execution state, which means that the in-memory "switch" to the new data may happen at different times for different connections (especially for isolation level repeatable-read).