Answer
Higher cardinality means more unique values, making indexes more selective and improving query performance.
Quick Answer
Index cardinality is the number of distinct values an indexed field has. High cardinality (user email, userId) = index is very selective = fast queries. Low cardinality (boolean, status with 3 values) = index is not selective = MongoDB may skip it and prefer a collection scan. Always index high-cardinality fields. Low-cardinality fields work better as second fields in compound indexes.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ