Change Streams in MongoDB 6.0 Support Pre- and Post-Image Retrieval, DDL operations, and more

Introduced with MongoDB 3.6, a MongoDB change stream is an API on top of the operations log (oplog) that allows users to subscribe their applications to data changes in a collection, database, or entire deployment. It makes it easy for teams to build event-driven applications or systems on MongoDB that capture and react to data changes in near real time — no middleware or database polling scripts required.

For MongoDB 6.0, we have enhanced change streams with new functionality that addresses a wider range of use cases while improving performance.

• Change streams now allow users to easily retrieve the before and after state of an entire document — sometimes referred to as pre- and post-images, respectively — when a document is either updated or deleted. Let’s suppose that you are storing user sessions in a collection and using a time-to-live (TTL) index to delete sessions as they expire. You can now reference data in the deleted documents to provide more information to the end user about their session after the fact. Or maybe you need to send an updated version of the entire document to a downstream system each time there is a data change. Added support for retrieving the before and after states of a document greatly expands the use cases change streams can address.

• Prior to MongoDB 6.0, change streams only supported data manipulation language (DML) operations. Change streams in MongoDB 6.0 will now support data definition language (DDL) operations such as creating and dropping indexes and collections so you can react to database events in addition to data changes.

• Change streams are built on MongoDB’s aggregation framework, which gives teams the capability to not only capture and react to data changes, but also to filter and transform the associated notifications as needed. With MongoDB 6.0, change streams that leverage filtering will have those stages automatically pushed to the optimal position within a change stream pipeline, dramatically improving performance.