RDS vs DynamoDB
Compare managed relational databases with managed NoSQL key-value and document storage in AWS.
Databases
Amazon RDS
Amazon RDS is a managed relational database service for engines like PostgreSQL, MySQL, and others. It is used for structured data, SQL queries, transactions, and relational models.
Databases
Amazon DynamoDB
Amazon DynamoDB is a managed NoSQL database designed for very high scale, predictable low latency, and key-value or document access patterns.
Key Differences
RDS is relational and SQL-based, while DynamoDB is NoSQL and optimized for key-value or document-oriented access.
RDS supports joins, transactions, and structured relational models, while DynamoDB is designed around access patterns rather than relational modeling.
DynamoDB is built for massive horizontal scale and low-latency reads and writes, while RDS is stronger for relational consistency and rich querying.
RDS requires schema design around tables and relationships, while DynamoDB requires careful partition key and access-pattern design.
DynamoDB removes much of the scaling complexity for high-throughput workloads, while RDS often needs more traditional database scaling strategies.
The choice depends more on data model and access patterns than on raw popularity.
When to Use
When to use RDS
Use RDS when your application relies on structured relational data, SQL queries, transactions, constraints, and strong table relationships.
When to use DynamoDB
Use DynamoDB when you need massive scale, predictable low latency, and data access built around well-defined key-based patterns rather than relational joins.
Tradeoffs
RDS is better for relational logic and SQL, but less naturally elastic for certain large-scale access models.
DynamoDB scales extremely well, but requires stronger discipline around partitioning and access-pattern design.
RDS is often better for relational business applications, while DynamoDB is often better for high-scale event, session, and lookup workloads.
Common Mistakes
Choosing DynamoDB without designing access patterns first.
Choosing RDS for workloads that need ultra-high key-value scale more than relational querying.
Treating NoSQL as automatically better just because it sounds more scalable.
Interview Tip
A strong short answer is: RDS is for relational SQL workloads, DynamoDB is for high-scale NoSQL access patterns.