How does MongoDB ensure high availability?

What is the default storage engine in MongoDB?

In MongoDB, which operator is used to query documents where a field contains an array with a specific value?

How does Redis handle expiration of keys?

A banking system using key-value storage keeps user balances under a single key. What’s the risk in concurrent transactions?

A food delivery app stores each customer’s last active GPS location. Which NoSQL model would be more efficient . Justify your answer in two or three words.

What is the drawback of range-based sharding in MongoDB?

Why is denormalization common in document databases?

Which consistency model is typically used in distributed key-value stores like Amazon Dynamo?