Aurora innovated by replacing the storage layer with a network store. Replicas don't need their own copy of the data (they point at the same network store) making replication lag almost non-existent. It means new replicas can be brought up in minutes. It allows really cool features like fast cloning and point in time recovery.

AlloyDB takes the same approach and adds some additional optimizations in query execution. It introduces a new caching layer and claims to use ML rather than a simple LRU cache. It also introduces cache-only representations of data in a columnar format, which allows it to greatly speed up analytical queries.