Consistency Guarantees

Linearizability vs. Serializability

These two terms are often confused, but they mean different things:

• Linearizability: A recency guarantee on a single object (register). It means that once a write completes, all later reads (by wall-clock time) return the new value. It makes the system look like a single variable.
• Serializability: An isolation property of transactions (groups of operations). It guarantees that the execution of transactions has the same effect as if they ran serially. It doesn't necessarily guarantee recency (you could be reading from a consistent snapshot of old data).

CAP Theorem

Consistency, Availability, Partition Tolerance. It's actually "Consistent or Available when Partitioned".

• Consistency here means Linearizability.
• Availability means every request gets a non-error response (but it might be stale).
• Partition Tolerance is not a choice; network partitions happen. You must choose between C and A.