Sorting can be expensive when MongoDB must collect many candidate documents and sort them in memory or use other supported execution resources. An appropriate index may allow the query to return records in the required order without a separate blocking sort.

Compound sort patterns must align with index ordering or its complete reverse in supported cases. Equality predicates on leading fields can make later index fields useful for sorting.

For example, { status: 1, createdAt: -1 } can support a query that matches one status and sorts by createdAt descending. A sort by unrelated fields may require a separate sort stage.

Use explain output to look for a sort stage and understand the selected plan. Do not assume that creating an index containing the sort field automatically eliminates sorting.

db.orders.createIndex({ status: 1, createdAt: -1 });

db.orders.find({ status: "delivered" })
  .sort({ createdAt: -1, _id: -1 })
  .limit(25)
  .explain("executionStats");