Policy Zones: How Meta enforces purpose limitation at scale in batch processing systems

This post introduces and details Policy Zones, a system for enforcing purpose limitations on data in large-scale batch processing systems. It integrates with Meta's exabyte-scale data warehouse and processing systems, using runtime enforcement and SQL parsing to propagate and enforce privacy annotations across millions of daily data flows. Policy Zones leverages Information Flow Control (IFC) principles to track data flow and enforce restrictions, ensuring downstream data restrictions are at least as restrictive as upstream sources. It also introduces Governable Data Annotations (GDAs) for precise, governed annotations on datasets and a Policy Zone Manager (PZM) to handle reclassification and prevent over-labeling. The post provides a walkthrough of how Policy Zones protects messaging data, highlighting its scale and technical implementation.