When should I learn compound indexes?
After single-field and unique indexes. Compound indexes are for multi-field queries. Learn the prefix rule (A, B, C serves A, A+B, A+B+C) and the ESR rule (equality, sort, range) for ordering fields.
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More FAQs in MongoDB Indexing Roadmap for Node.js Developers
Understand why, single-field indexes, unique indexes, compound indexes (prefix and ESR rules), explain(), .lean() and .select(), cursor-based pagination, text indexes, TTL indexes, index tradeoffs, and monitoring in production.
Why they matter. Without indexes, MongoDB scans every document. For small collections, fine; for large, slow. Indexes are how you scale reads. Then learn single-field indexes and verify with explain().
When offsets get large. Skip is slow for large offsets because MongoDB scans the skipped docs. Cursor-based pagination finds documents where createdAt is less than the last cursor. Needs an index on the cursor field.
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