AWS RDS vs DynamoDB – When to Use Which

AWS RDS vs DynamoDB

• AWS offers both relational (RDS/Aurora) and NoSQL (DynamoDB) managed database services.
• Choosing between them depends on data model, access patterns, scale requirements, and consistency needs.
• Many architectures use both — RDS for transactional data and DynamoDB for high-scale, low-latency access patterns.

RDS vs DynamoDB Comparison

When to Choose RDS / Aurora

• Complex queries — need SQL JOINs, aggregations, subqueries, window functions.
• ACID transactions — financial systems, order processing, inventory management.
• Existing relational schema — migrating from on-premises MySQL/PostgreSQL/Oracle/SQL Server.
• Reporting workloads — need ad-hoc queries across multiple tables.
• Normalized data model — relationships between entities are primary concern.
• Moderate scale — up to hundreds of thousands of requests/second (Aurora).
• Examples: E-commerce orders, banking, ERP, CMS with complex relationships.

When to Choose DynamoDB

• Known access patterns — you can design a key schema around how data is queried.
• Massive scale — millions of requests/second with consistent single-digit millisecond latency.
• Simple key-value or document lookups — get/put by primary key.
• Serverless / event-driven architectures — pairs naturally with Lambda.
• Global applications — multi-Region active-active with Global Tables.
• Variable/spiky traffic — on-demand mode handles any traffic without pre-provisioning.
• Zero operational overhead — no patching, no maintenance windows.
• Examples: Gaming leaderboards, session stores, IoT data, shopping carts, user profiles.

Using Both Together

• Common pattern: RDS for source of truth (transactions) + DynamoDB for read-heavy access (caching, APIs).
• Use DynamoDB Streams + Lambda to sync DynamoDB changes to RDS (or vice versa).
• Use zero-ETL from Aurora/DynamoDB to Redshift for unified analytics.
• Example: E-commerce — RDS for order processing, DynamoDB for product catalog and session data.

AWS Certification Exam Practice Questions

1. A social media application needs to store user profiles and serve them with single-digit millisecond latency at millions of requests per second globally. Which database is most appropriate?
   1. Aurora PostgreSQL with read replicas
   2. DynamoDB with Global Tables
   3. RDS MySQL Multi-AZ
   4. ElastiCache Redis
2. A financial application requires complex multi-table transactions where a transfer must debit one account and credit another atomically, with full SQL reporting capabilities. Which is most appropriate?
   1. DynamoDB with TransactWriteItems
   2. Aurora PostgreSQL with Multi-AZ
   3. DynamoDB with DAX
   4. Aurora Serverless with DynamoDB Streams
3. A startup wants to minimize operational overhead with zero maintenance, pay only for actual usage, and handle unpredictable traffic spikes from 0 to 100K requests/second. Which option is best?
   1. Aurora Serverless v2
   2. DynamoDB On-Demand mode
   3. RDS with Auto Scaling read replicas
   4. Aurora with Provisioned capacity
4. An analytics team needs to run complex ad-hoc SQL queries with JOINs across customer, order, and product tables without knowing access patterns in advance. Which is appropriate?
   1. DynamoDB with GSIs
   2. DynamoDB with PartiQL
   3. Aurora PostgreSQL
   4. DynamoDB export to S3 + Athena
5. A gaming company stores player sessions in DynamoDB and order history in Aurora. They want unified analytics across both datasets without ETL pipelines. Which feature enables this?
   1. DynamoDB Streams to Aurora via Lambda
   2. Zero-ETL from both Aurora and DynamoDB to Redshift
   3. DynamoDB export to S3 + Aurora export to S3
   4. Federated queries in Athena

Related Posts

• AWS DynamoDB
• AWS RDS Aurora
• AWS Aurora vs RDS
• AWS DynamoDB vs DocumentDB vs Neptune
• AWS Database Services Cheat Sheet

References

Amazon DynamoDB Developer Guide

Amazon Aurora User Guide