MongoDB Data Modeling Flashcards

What is the 'subset pattern' in MongoDB data modeling?

Answer: Storing only the most frequently accessed subset of a large array in the main document

The subset pattern splits frequently accessed array elements (like recent reviews) into the main document, keeping the full array in a separate collection.

What is the main advantage of using ObjectId as the _id field in MongoDB?

Answer: It is automatically generated, globally unique, and contains a timestamp

ObjectId is a 12-byte identifier automatically generated by MongoDB drivers, containing a timestamp, machine ID, process ID, and random counter ensuring uniqueness.

In MongoDB, what does 'schema-on-read' mean?

Answer: The application interprets document structure at read time rather than enforcing it at write time

Schema-on-read means MongoDB stores any document structure and the application code is responsible for interpreting the data's shape when reading.

What is a GridFS in MongoDB?

Answer: A specification for storing files larger than 16 MB by splitting them into chunks

GridFS is a MongoDB specification that stores large files by dividing them into 255 KB chunks stored in fs.chunks, with metadata in fs.files.

What is the 'versioning pattern' in MongoDB used for?

Answer: Maintaining historical versions of a document by preserving previous states

The versioning pattern keeps previous versions of a document (in the same or a separate collection) to support audit trails, history, and rollback capabilities.

What does the 'approximation pattern' optimize in MongoDB?

Answer: Reduces write operations by approximating counters instead of updating on every event

The approximation pattern reduces write load by updating counters or statistics only periodically rather than on every event, trading perfect accuracy for performance.