My next post will be about Amazon DocumentDB and how it compares to MongoDB in terms of indexing a flexible schema with multiple keys. There's a lot of confusion today with the "DocumentDB" name because earlier this year Microsoft announced DocumentDB: Open-Source Announcement which has nothing to do with Amazon DocumentDB.
Amazon DocumentDB is a managed NoSQL database service that supports document data structures and is compatible with MongoDB versions 3.6, 4.0, and 5.0. It allows users to store, query, and index JSON data. Its storage capabilities resemble those of Amazon Aurora, featuring compute and storage separation, a monolithic read-write node, up to 15 read-only replicas, and multi-AZ storage. There are guesses that the API is built on PostgreSQL and, which, if true, brings another similarity with the Microsoft DocumentDB extension for PostgreSQL.
DocumentDB is the name of a PostgreSQL extension used by Microsoft in vCore-based Azure Cosmos DB for MongoDB to emulate some MongoDB capabilities with BSON and RUM indexes.
You might wonder how Microsoft, in 2025, adopted a name already in use by a similar product released six years earlier by its main competitor. Actually, Microsoft "owned" this name and built a DocumentDB service long before in 2013. Let's use the Web Archive to do some archeology.
- In 2011 the
documentdb.comdomain was for sale
in 2012 Microsoft registered the domain
in 2013 Microsoft was probably building a document data store product and prepared a web site for it
in 2014 they have put a page with generic content about NoSQL, JSON and document databases, probably to boost SEO before releasing the product. It doesn't mention Microsoft, but one video shows documents in Word and Access.
The other video "Why Choose NoSQL and Document Databases over RDBMS" by Michael Kennedy / LearningLine, although 12 years old, remains relevant in today’s discussion of database technologies. Especially the simplicity of the document model:
Later, the www.documentdb.com redirected to http://azure.microsoft.com/en-us/services/documentdb and then to http://azure.microsoft.com/en-us/services/cosmos-db.
The product went through a MongoDB-like protocol on top of DocumentDB
Microsoft has a history of renaming services that never went popular in order to attract a broader audience. There's also another PostgreSQL with another extension (Citus) in CosmosDB, which has nothing to do with the PostgreSQL DocumentDB extension used by the vCore-based Azure Cosmos DB for MongoDB. CosmosDB is a marketing umbrella for many different technologies, adding to the confusion.
I hope that clears up some confusion. The best way to refer to the AWS service is as "Amazon DocumentDB", and when discussing the BSON emulation with RUM indexes that powers the Microsoft Azure service, it should be called the "DocumentDB PostgreSQL extension".
