Explanation:
Box 1: Azure Database for PostgreSQL Flexible Server
For horizontal scaling of transactional writes in Azure PostgreSQL using row-based sharding, you should utilize Azure Database for PostgreSQL Flexible Server with Elastic Clusters. This feature leverages the Citus extension for PostgreSQL, enabling you to shard your data across multiple nodes and manage them as a single, distributed database.
Box 2: Distributed tables
Azure Database for PostgreSQL Flexible Server uses distributed tables for scaling through the use of an Elastic cluster, powered by the Citus extension. This allows for scaling out by adding more nodes to the cluster and distributing data across them, rather than just increasing the compute power of a single node.
Reference:
https://techcommunity.microsoft.com/blog/adforpostgresql/postgres-horizontal-scaling-with- elastic-clusters-on-azure-database-for-postgres/4303508