Azure HorizonDB is a cloud-native, 100% PostgreSQL-compatible database currently in preview on Azure. It forks PostgreSQL and disaggregates compute from storage, using a 'database as a log' architecture with a dedicated write-ahead log (WAL) storage fleet and a separate data storage fleet, both backed by zone-redundant blob storage. This design enables up to 192 vCores on the primary, up to 15 read replicas, 128 TB max storage (auto-scaling), and fast failover without traditional PostgreSQL replication. Applications require zero code changes since the API is fully PostgreSQL-compatible. Additional features include Entra ID authentication, 75+ PostgreSQL extensions (pgvector, DiskANN, BM25), Microsoft Fabric mirroring, AI pipeline support via SQL, and model management through Microsoft Foundry. Pricing covers compute, optional standbys, storage, and backups, with no separate IOPS charges. The service is currently in preview and not recommended for production use.