MongoDB is the trending NoSQL database, with significant adoption among the Fortune 500 and Global 500. Follow along and check our list of 83 common MongoDB interview questions and answers and get ready for your next NoSQL developer interview in 2021.
You can also find all 83 answers here 👉🏼 https://devinterview.io/dev/mongodb-interview-questions
MongoDB is an open-source document database that provides high performance, high availability, and automatic scaling. It's Key Features are:
- Document Oriented and NoSQL database.
- Supports Aggregation
- Uses BSON format
- Sharding (Helps in Horizontal Scalability)
- Supports Ad Hoc Queries
- Schema Less
- Capped Collection
- Indexing (Any field in MongoDB can be indexed)
- MongoDB Replica Set (Provides high availability)
- Supports Multiple Storage Engines
- Flexible data model in form of documents
- Agile and highly scalable database
- Faster than traditional databases
- Expressive query language
You should consider embedding documents for:
- contains relationships between entities
- One-to-many relationships
- Performance reasons
SQL databases store data in form of tables, rows, columns and records. This data is stored in a pre-defined data model which is not very much flexible for today's real-world highly growing applications. MongoDB in contrast uses a flexible structure which can be easily modified and extended.
MongoDB uses a database profiler to perform characteristics of each operation against the database. You can use a profiler to find queries and write operations
MongoDB stores BSON (Binary Interchange and Structure Object Notation) objects in the collection. The concatenation of the collection name and database name is called a namespace
Indexes support the efficient execution of queries in MongoDB. Without indexes, MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement. If an appropriate index exists for a query, MongoDB can use the index to limit the number of documents it must inspect.
BSON is a binary serialization format used to store documents and make remote procedure calls in MongoDB. BSON extends the JSON model to provide additional data types, ordered fields, and to be efficient for encoding and decoding within different languages.
It is a group of mongo instances that maintain same data set. Replica sets provide redundancy and high availability, and are the basis for all production deployments.
The ideas of a replicaset are :
- Every data are repartited on each node
- Only one node accept writes
Replication is the process of synchronizing data across multiple servers. Replication provides redundancy and increases data availability. With multiple copies of data on different database servers, replication protects a database from the loss of a single server. Replication also allows you to recover from hardware failure and service interruptions.
ObjectIds are small, likely unique, fast to generate, and ordered. ObjectId values consist of 12 bytes, where the first four bytes are a timestamp that reflect the ObjectId’s creation. Specifically:
- a 4-byte value representing the seconds since the Unix epoch,
- a 5-byte random value, and
- a 3-byte counter, starting with a random value. In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. If an inserted document omits the _id field, the MongoDB driver automatically generates an ObjectId for the _id field.