Backend & systems·Transactions and isolation
you wrap the two updates in a transaction so either both land or neither does, and nobody sees the halfway state.
ACID
Atomicity, consistency, isolation and durability: the guarantees a transactional database makes about a unit of work. In practice only atomicity and durability are absolute; isolation is a dial you set and consistency is mostly your constraints, not the database's opinion. Knowing which of the four you actually rely on is what makes the acronym useful rather than decorative.