Document Databases (MongoDB, Couchbase)

Question 1

What is MongoDB?

Answer 1

MongoDB is a NoSQL, document-oriented database that stores data in flexible, JSON-like documents.

Question 2

What is the document model in MongoDB?

Answer 2

The document model stores data as BSON documents which can include nested fields and arrays, allowing for more natural data modeling.

Question 3

What is BSON in MongoDB?

Answer 3

BSON (Binary JSON) is a binary format used to store documents in MongoDB, supporting additional data types like Date and BinData.

Question 4

How do MongoDB collections compare to relational database tables?

Answer 4

Collections are analogous to tables, but they do not enforce a schema, allowing documents with different structures in the same collection.

Question 5

What is schema design in MongoDB?

Answer 5

Schema design in MongoDB involves structuring documents and collections to optimize for queries, updates, and scaling.

Question 6

What is the purpose of insertOne in MongoDB?

Answer 6

insertOne is a CRUD operation that adds a single document to a collection.

Question 7

What does find do in MongoDB?

Answer 7

find retrieves documents from a collection that match specified query criteria.

Question 8

What does updateOne do in MongoDB?

Answer 8

updateOne modifies the first document that matches the filter criteria in a collection.

Question 9

What does deleteOne do in MongoDB?

Answer 9

deleteOne removes the first document that matches the filter criteria from a collection.

Question 10

How do you query nested fields in MongoDB?

Answer 10

Use dot notation, like find({ 'address.city': 'New York' }), to query nested fields.

Question 11

How do you query arrays in MongoDB?

Answer 11

You can use operators like $elemMatch or $in to query array fields.

Question 12

What are indexes in MongoDB?

Answer 12

Indexes improve query performance by allowing efficient data retrieval without scanning all documents.

Question 13

What types of indexes does MongoDB support?

Answer 13

MongoDB supports single-field, compound, multikey, geospatial, text, and hashed indexes.

Question 14

What is the aggregation pipeline in MongoDB?

Answer 14

A framework that processes documents through multiple stages like $match, $group, $project, etc., to transform and analyze data.

Question 15

What is the purpose of transactions in MongoDB?

Answer 15

Transactions ensure that multiple operations across multiple documents execute as a single atomic unit, preserving data integrity.

Question 16

What is replication in MongoDB?

Answer 16

Replication copies data from a primary node to secondary nodes, ensuring high availability and data redundancy.

Question 17

What is sharding in MongoDB?

Answer 17

Sharding distributes data across multiple machines (shards) to support horizontal scaling of large datasets.

Question 18

What are document databases?

Answer 18

Document databases store data in document format (JSON, BSON, XML), and each document is a self-contained unit of data.

Question 19

What are examples of document databases?

Answer 19

Examples include MongoDB, Couchbase, and Amazon DocumentDB.

Question 20

What are the advantages of document databases?

Answer 20

Advantages include flexible schema, faster development, natural data modeling, and easier horizontal scaling.

Question 21

What are the disadvantages of document databases?

Answer 21

Disadvantages include data duplication, limited support for complex joins, and higher memory usage.

Question 22

What are best practices for MongoDB schema design?

Answer 22

Model around application query patterns, embed related data when access is frequent, avoid deeply nested documents, and use proper indexing.

Question 23

When should you embed documents in MongoDB?

Answer 23

Embed when the relationship is one-to-few and data is accessed together, like a user and their addresses.

Question 24

When should you reference documents in MongoDB?

Answer 24

Reference when the relationship is one-to-many or many-to-many and data is accessed independently.

Question 25

What are common use cases for MongoDB?

Answer 25

Content management, IoT, real-time analytics, mobile backends, catalogs, and personalization engines.

Question 26

How does MongoDB affect system design?

Answer 26

It encourages flexible schema design, horizontal scalability, denormalization, and microservices-friendly architecture.

Question 27

Give an example MongoDB document.

Answer 27

{ \"name\": \"John\", \"email\": \"john@example.com\", \"orders\": [ { \"item\": \"Book\", \"price\": 10 } ] }

Question 28

What are architectural implications of using MongoDB?

Answer 28

MongoDB enables scalable, distributed systems with eventual consistency, and often requires designing around trade-offs in data modeling.

Question 29

What is MongoDB's performance under high load?

Answer 29

It performs well with proper indexing and schema design, and supports scaling with sharding and replication.

Question 30

How does MongoDB ensure fault tolerance?

Answer 30

Through replica sets, automatic failover, and self-healing nodes in case of crashes or maintenance.

Question 31

How can you monitor MongoDB?

Answer 31

Using tools like MongoDB Atlas, Ops Manager, `mongostat`, and `mongotop` to monitor performance and resource usage.

Question 32

How do you debug slow queries in MongoDB?

Answer 32

Use `explain()` to analyze query plans and the profiler to identify and log slow operations.

Question 33

What are real-world tradeoffs with MongoDB?

Answer 33

Tradeoffs include faster dev and flexibility vs. increased complexity in enforcing consistency and handling joins.

Question 34

What are common MongoDB interview questions?

Answer 34

Examples: 'Explain the aggregation pipeline', 'When to embed vs. reference?', 'How does sharding work?', 'Explain replica sets'.

Question 35

What are potential gotchas with MongoDB?

Answer 35

Unbounded document growth, missing indexes causing slow queries, misuse of sharding keys, and lack of enforced schema leading to inconsistent data.