By default, MongoDB created the _id collection for every collection.

Just Dial

Software Engineer

How many indexes does MongoDB create by default for a new collection?

Just like in traditional RDBMSes, updating documents is fast for normalized data and relatively slower for denormalized data. On the other hand, reading documents is fast in denormalized data and slower for normalized data. Denormalized data is harder to keep in sync and takes up more space.

Note that in MongoDB, denormalized data is a more common expectation. This is because RDBMSes have inherent support for normalization and allow data to be managed as a separate concern, whereas NoSQL DBMSes like MongoDB do not inherently support normalization.

Instead, normalization requires that client applications carefully maintain integrity themselves. To help with this, it’s possible to run audits to ensure that app data conforms to expected patterns of referential integrity.

Normalising data in a MongoDB database?

Both sharding and replication involve using more than one instance to host the database.

Replicas are MongoDB instances with the same data, hence the name. We use replicas to increase redundancy and availability.

With sharding, on the other hand, each shard instance has different data from its neighbors. We use sharding for horizontal scaling.

Top Mongodb Interview Questions

1. How many indexes does MongoDB create by default for a new collection?

2. Normalising data in a MongoDB database?

3. How are sharding and replication similar to each other in MongoDB, and how are they different?