Should I index every field in MongoDB?
No. Each index adds overhead to writes and uses storage. Index only the fields you query often. Over-indexing slows down writes without benefit. Use the explain method to confirm which indexes are actually used by your queries.
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More FAQs in MongoDB Indexing Best Practices for Node.js Apps
Index fields you query often: email for login, userIds for fetching a user's data, and foreign keys. For multi-field queries, use compound indexes. For sorts, index the sort field. Use the explain method to confirm indexes are used.
An index on multiple fields together, like { status: 1, age: 1 }. Use it when you query on multiple fields together, like { status: 'active', age: { $gt: 18 } }. The order of fields in the compound index matters for query performance.
Run User.find(query).explain('executionStats'). If it shows IXSCAN, the index is used. If it shows COLLSCAN, MongoDB is scanning the entire collection, which means your index is not being used for this query.
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