Answer
An index improves search performance on fields. Without indexes, MongoDB performs collection scans.
Quick Answer
An index in MongoDB is a data structure (B-tree) that speeds up queries by allowing MongoDB to find documents without scanning the entire collection. Without an index, every query does a full collection scan (COLLSCAN). Create an index on frequently queried fields: db.users.createIndex({email: 1}). Too many indexes slow down writes.
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SugharaIQ Editorial Team
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Source: SugharaIQ