Choosing a Database in System Design Interviews

Types of Databases

• SQL Databases
  • Stand for Structured Query Language
  • Table-based
• NoSQL Databases
  • Types: Document, Key-Value, Graph, Wide Column stores

Key Differences

• Scalability
  • SQL: Vertically scalable
  • NoSQL: Horizontally scalable

Strengths of SQL Databases

• Relational
  • Easy querying on relationships between data
  • Effective data organization and structuring
• Structured Data
  • Reduced room for error
  • Requires known data model and format before storage
• ACID Compliance
  • Atomic: Transactions are fully completed or not at all
  • Consistent: Ensures data integrity
  • Isolated: Transactions are processed independently
  • Durable: Transactions are permanent once completed

Weaknesses of SQL Databases

• Structured Data Setup
  • Requires pre-defined tables and columns, increasing setup time
• Scalability Issues
  • Difficult to scale horizontally
  • More expensive to scale vertically for write-heavy systems

Benefits of NoSQL Databases

• Flexibility
  • Simple setup without table relationships
  • Better for unstructured data
• Horizontal Scaling
  • Can shard data across data stores for distributed databases
  • Handles very large amounts of data without expensive servers

Weaknesses of NoSQL Databases

• Eventual Consistency
  • Designed for distributed systems
  • Writes may not be immediately reflected across all nodes
  • Reads can return stale data during replication delays

Conclusion

• NoSQL databases can be strongly consistent if limited to a single shard but lose this benefit when distributed

Tips

• Choose the right database type based on use case and required features (e.g., consistency vs. scalability)

Further Learning

• Check out the Exponent article linked in the description for more details