Command summary:
db.collection.createIndex( { <fieldname> : ( 1 | -1 ) } );
Creating indexes is an easy way to improve MongoDB performance at the collection level. Indexes can be created on a single field, multiple fields, or embedded fields within arrays or objects. When you issue a query which involves the indexed field, MongoDB is able to use information stored in the index rather than having to do a full scan of all database documents. In this sense, you can think of the index as a shortcut which saves time when producing query results.
There are three index types supported by MongoDB: single field (https://docs.mongodb.com/manual/core/index-single/#single-field-indexes), compound (https://docs.mongodb.com/manual/core/index-compound/#compound-indexes), and multi-key (https://docs.mongodb.com/manual/core/index-multikey/#multikey-indexes).
Each of these can be...