Question 1

What's the difference between MongoDB and MySQL (relational databases)?

Accepted Answer

MongoDB is a NoSQL document database that stores data as flexible JSON-like documents (BSON). MySQL is a relational database that stores data in tables with predefined columns and uses joins to relate data. MongoDB is often easier when your data shape changes frequently or varies by record, while MySQL is often a strong fit for highly structured data, complex joins, and strict relational constraints.

Question 2

When should I use MongoDB?

Accepted Answer

Use MongoDB when you need flexible schemas, fast iteration, and data that naturally fits a document model—such as user profiles, product catalogs, content management, event tracking, and IoT payloads. It’s also a good fit when you want to scale reads/writes horizontally and avoid frequent schema migrations. Consider alternatives if you rely heavily on multi-table joins, strict relational constraints, or complex transactional reporting across many entities.

Question 3

How much does MongoDB cost?

Accepted Answer

Cost depends on how you run it. Self-managed MongoDB is free to download, but you pay for infrastructure (VMs/containers), storage, backups, and operations time. Managed options (like MongoDB Atlas) charge based on cluster tier (CPU/RAM), storage size and IOPS, backup retention, data transfer, and optional features (e.g., dedicated clusters, multi-region replication). Cloud-provider “MongoDB-compatible” services (like Amazon DocumentDB or Cosmos DB’s MongoDB options) have their own pricing based on instance/throughput, storage, and I/O.

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