By completing this chapter, you should understand why indexes matter, how single-field and compound indexes work, compound prefixes, ESR, sort support, covered queries, multikey indexes, unique indexes, partial and sparse indexes, TTL indexes, text indexes, geospatial indexes, hashed and wildcard indexes, hidden indexes, selectivity, explain output, index intersection, index lifecycle management, and production index design.

Before moving forward, choose a real query from an application, record its filter, sort, projection, and expected result size, inspect its execution plan, propose an index, and test it against realistic data. Explain both the benefit and the cost of the index.

You are ready when you can explain why an index matches a query pattern, which prefix it supports, whether it can satisfy the sort, whether the query can be covered, and what evidence demonstrates that the index improves the workload.