Snowflake argues that true data interoperability requires bidirectional support for the Iceberg REST Catalog protocol, including both inbound and outbound federation with vended credentials. Databricks Unity Catalog is criticized for supporting only inbound federation, using JDBC and long-lived IAM credentials for outbound access rather than the open Iceberg REST standard, and restricting writes to external catalog tables. Snowflake Horizon Catalog, built on Apache Polaris, is presented as implementing the full Iceberg REST Catalog spec bidirectionally, including per-query vended credentials and fine-grained row/column access controls via the Scan Plan API. The post also notes that Databricks compute can still achieve full read/write access to Iceberg REST-compliant catalogs when Unity Catalog is disabled.
