MongoDB has become the standard API for document databases, and today’s users expect more freedom, open source solutions, and portability. Over the years, the ecosystem has responded with various alternatives, including Amazon DocumentDB, which emulates MongoDB on AWS, JSONB and the SQL/JSON standard in PostgreSQL core, libraries like Pongo, and compatibility layers such as FerretDB.

Recently, Microsoft open-sourced DocumentDB, a MongoDB-compatible extension for PostgreSQL. This solution, proven at scale in Azure, is now governed by the Linux Foundation to build an open, vendor-neutral community and rely on the PostgreSQL ecosystem.

This presentation goes through how this extension actually works. It adds BSON data types and extended RUM indexing to PostgreSQL, along with a document API, and a Rust-based gateway implementing MongoDB’s wire protocol. This is a key difference from JSONB-based approaches, as compatibility is handled at the protocol level, not only through SQL. We will also look at how indexing evolved, what changed recently, and the trade-offs involved—when a document model makes sense, and when it doesn’t.