What does 'IXSCAN' represent in a query plan?

The term 'IXSCAN' in a MongoDB query plan indicates an index scan. This occurs when MongoDB uses an index to efficiently retrieve data instead of scanning every document in a collection, which would be a collection scan. When an index is utilized, the database can quickly locate the relevant documents based on the indexed fields, leading to improved query performance.

Using an index scan is beneficial for performance, especially on large datasets, as it reduces the amount of data that MongoDB needs to process. During an index scan, MongoDB traverses the index structure, which is typically more compact than the actual data in the collection. This allows the query to be resolved much faster than if every document had to be examined.

Other options relate to different operations in MongoDB. For instance, collection scans involve checking every document in a collection and are generally less efficient. Sort operations are about organizing the results of a query, while fetch operations refer to retrieving documents after identifying them through an index. Each plays a different role in query execution, but 'IXSCAN' specifically and directly refers to the process of scanning an index to find documents.