What are indexes in MongoDB?

Indexes in MongoDB are indeed ordered data structures that store a portion of the data, specifically references to documents within a collection. This allows for efficient querying, sorting, and retrieval of data, as indexes enable MongoDB to quickly locate the specific documents that match the query criteria.

When working with large datasets, fetching documents without indexes can result in a full collection scan, which is time-consuming. With indexes, MongoDB can reduce the amount of data it needs to search through by providing a structured way to access the relevant documents more swiftly. An index functions similarly to an index in a book, guiding the database engine to the correct page (document) without needing to look through every page (document) sequentially.

The efficiency provided by indexes is crucial in optimizing database performance, especially as the size of the data grows. By maintaining a portion of the data in an ordered manner, MongoDB can enhance the execution speed of queries, achieving better response times for applications that rely on quick data access.