MongoDB - Associate Developer Study Guide

3: Indexes

This chapter walks the MongoDB indexing surface a working application developer must control: which index type fits which query shape, how the ESR rule orders fields in a compound index, how index prefixes decide whether a query is supported, when a projection produces a covered query, and how to read `explain()` output to distinguish `IXSCAN` from `COLLSCAN` and evaluate `totalKeysExamined` versus `totalDocsExamined`. Every construct is anchored to `mongosh` commands and driver-level equivalents, with attention to the property flags (unique, partial, sparse, TTL, collation) that shape which documents an index tracks.