Why should equality predicates be prioritized in a compound index?

Prioritizing equality predicates in a compound index is crucial because they significantly enhance query performance by reducing the number of documents that need to be scanned to satisfy a query. When a query includes equality conditions, the database engine can quickly locate the specific documents that match those conditions, minimizing the search space.

This efficient retrieval happens because compound indexes organize data in a way that allows the database to take full advantage of the equality predicates, leading to a more direct access path to the relevant documents. Consequently, when the query engine can narrow down the results using equality predicates early in the processing, it can reduce the overall workload, thus lowering the query time significantly.

While other factors, such as the overall design of the database structure, may play a role in performance, the initial reduction of candidate documents directly translates to faster execution times and improved efficiency, making this approach an effective optimization strategy.