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  • Geeta Gharpure thinks this is interesting:

  1. ndexes significantly reduce the amount of work required to fetch documents. Without the proper indexes, the only way to satisfy a query is to scan all documents linearly until the query conditions are met. This frequently means scanning entire collections.
  2. Only one single-key index will be used to resolve a query.[1] For queries containing multiple keys (say, ingredient and recipe name), a compound index containing those keys will best resolve the query.

    From

    Cover of MongoDB in Action

    Note

    Index, Single vs compound, compound redundancy, compound order