MongoDB vs PostgreSQL: When to Use Each

MongoDB vs PostgreSQL

Choosing the right database for your application.

Data Model

MongoDB for flexible documents. PostgreSQL for relational data with JSONB support.

PostgreSQL Strengths

PostgreSQL is the best long-term choice with no vendor lock-in. It supports advanced indexing (partial indexes, bloom indexes) and can scale horizontally with Citus for distributed SQL.

MySQL and MariaDB

MySQL is easier to get started with, cloud-friendly, fully ACID-compliant, and supports horizontal sharding via MySQL Cluster. MariaDB is an open-source, drop-in MySQL replacement with community-driven development and additional storage engines.

MongoDB Deep Dive

MongoDB stores data as document/BSON format, supports auto-sharding out of the box, provides a powerful aggregation pipeline for analytics, and by design does not support joins (use embedding or application-level lookups instead).

DynamoDB

DynamoDB is AWS's serverless NoSQL database with single-digit millisecond latency at any scale. It supports ACID transactions and is the default database when using AWS Amplify.

Amazon Aurora

Aurora delivers higher performance than standard RDS instances, better fault tolerance with six-way replication, and faster recovery times. The tradeoff is that Aurora costs more than standard RDS.

SQL vs NoSQL Scaling

Horizontal scaling beats vertical scaling for most high-traffic applications. NoSQL databases handle schema evolution better since documents can have varying structures without requiring migrations.

Performance

MongoDB for read-heavy, denormalized data. PostgreSQL for complex queries and joins.

Scaling

MongoDB shards natively. PostgreSQL scales vertically with read replicas.

RDS Instance Classes

Burstable instances (db.t2, db.t3, db.t4g) are ideal for development and testing. Memory Optimized instances (db.r5) are suited for production workloads with high memory demands. General Purpose instances (db.m5, db.m5d) handle enterprise-grade applications with balanced compute and memory.

RDS Storage Tiers

RDS offers three storage types in ascending performance: Magnetic (legacy, avoid for new deployments), General Purpose SSD gp2 (baseline with 3000 IOPS burst), and Provisioned IOPS SSD io1 (consistent throughput for I/O-intensive workloads). Maximum storage capacity is 64 TiB for MySQL, PostgreSQL, and Oracle, and 16 TiB for SQL Server.

EC2 to RDS Security

Create a dedicated RDS security group with inbound rules allowing MySQL/Aurora TCP port 3306 from your EC2 security group and your admin IP address. Never expose RDS directly to the public internet.

SSH Tunnel to RDS

Use MySQL Workbench with Standard TCP/IP over SSH. Set the EC2 public IP as the SSH host and the RDS private DNS endpoint as the MySQL host. This keeps your RDS instance in a private subnet while still allowing secure access.

Recommendation

PostgreSQL for most applications. MongoDB for specific document-heavy use cases.