What does 'FETCH' signify in a query plan?

In the context of a query plan in MongoDB, 'FETCH' refers specifically to the operation where documents are being read from the collection based on the criteria defined in the query. When a query is executed, MongoDB may first determine which documents match the query conditions by using the index if one exists. After identifying potential matches, the 'FETCH' phase involves retrieving the full documents that correspond to those identifiers.

This step is crucial because, although the database engine can quickly identify documents through indexing, it still needs to fetch the complete document data from the collection to return the necessary results to the client. The overall efficiency and performance of the database operations can be greatly influenced by how well this FETCH operation is optimized, particularly in scenarios with large datasets or complex queries.

While other terms related to query execution exist, such as sorting and scanning, they do not describe the act of reading documents from storage in the same manner that FETCH does. For example, sorting involves arranging the fetched results in a specific order based on specified criteria, and scanning could refer to accessing documents without the benefit of an index, which is not the case during the FETCH phase. Thus, identifying 'FETCH' as the stage where documents are being read is accurate and aligns with the