YugabyteDB is a 100% open source, distributed SQL database system that utilizes a two-layer architecture to achieve its goals. This architecture consists of an extensible query processing layer and a distributed document store, which provides strong consistency with global secondary indexes. The query processing layer, referred to as YSQL, allows for stateless processing without the constraints of synchronizing states and caches across multiple nodes. This statelessness enables complex features that are only possible with this architecture, including support for complex SQL features such as multi-row and multi-table operations. YugabyteDB's two-layer architecture is compared favorably to other databases, including Oracle RAC and Amazon Aurora, which have limitations in terms of scalability and availability. Additionally, YugabyteDB's query processing layer reuses PostgreSQL, allowing access to its feature-rich ecosystem while maintaining a stateless design that enables true scale-out capabilities. The distributed document store, or DocDB, distributes data across multiple servers and allows for fully consistent cross-node transactions, providing strong consistency with global secondary indexes. This architecture also provides logical replication, which is simpler and more autonomous than traditional physical replication methods, allowing for greater agility in the cloud-native environment. Overall, YugabyteDB's two-layer architecture represents a significant innovation in distributed SQL databases, enabling true scale-out capabilities while maintaining strong consistency and availability.