What does the command db.collection.countDocuments() do?

The command db.collection.countDocuments() is used to accurately count the number of documents stored within a specific collection in a MongoDB database. This command is particularly useful because it returns the total number of documents that match a query filter, allowing developers to know how many records are present without needing to fetch the actual documents themselves. This can improve performance, especially in large collections, where retrieving all documents can be inefficient.

The countDocuments command is a reliable way to achieve this since it does not include any deleted documents and provides a count based on the current state of the collection. It is designed to operate correctly in the context of MongoDB's concurrency model, ensuring that the count reflects the most recent data available. This command is essential for analytics and reporting tasks, where understanding the number of records is fundamental for further processing.