limits of number of collections in databases

Question

Can anyone say are there any practical limits for the number of collections in mongodb? They write here https://docs.mongodb.com/manual/core/data-model-operations/#large-num

Answer 1

A little background:

Every time mongo creates a database, it creates a namespace (db.ns) file for it. The namespace (or collections as you might want to call it) file holds the metadata about the collection. By default the namespace file is 16MB in size, though you can increase the size manually. The metadata for each collections is 648 bytes + some overhead bytes. Divide that by 16MB and you get approximately 24000 namespaces per database. You can start mongo by specifying a larger namespace file and that will let you create more collections per database.

The idea behind any default configuration is to not bother the user with every single detail (and configurable knob) and choose one that generally works for most people. Also, viability does go hand in hand with best/good design practices. As Chris said, consider the shape of your data and decide accordingly.