Spanner uses a hierarchical table model instead, where a parent table key is a strict prefix of the child table key. https://cloud.google.com/spanner/docs/sche

Spanner uses a hierarchical table model instead, where a parent table key is a strict prefix of the child table key. https://cloud.google.com/spanner/docs/schema-and-data-model#creating_a_hierarchy_of_interleaved_tables https://cloud.google.com/spanner/docs/schema-and-data-model#... From a technical perspective, I'd guess that the reason was because it makes local transactions trickier to do. Spanner has a philosophy of avoiding work that isn't required, and knows how to optimize transactions that don't require 2PC-ing data on different servers.