Is the advantage of calling ensureindex in mongodb just speed? -

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i've been reading ensureindex (mongodb: when call ensureindex?) , (pymongo / mongodb: create index or ensure index?) , mongodb documentation, havent come conclusion use of ensureindex. doesnt mongodb create id every document? why need index? in case have document this:

{     "name": "jon secada",     "date of birth": "09-19-1983",     "address": "1 chemin des loges",     "city": "versailles" }

whats advantage of calling ensureindex on "name" example?

you gain more efficient searches on fields choose @ cost of additional memory , disk space consumed.


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