Amazon DynamoDB Overview

AWS Amplify Gen 2 uses Amazon DynamoDB as its data store. Let's understand what DynamoDB is and why it's a great choice for modern applications.

What is DynamoDB?

Amazon DynamoDB is a fully managed NoSQL database service provided by AWS. Unlike traditional relational databases (like MySQL or PostgreSQL), DynamoDB stores data in a flexible, document-like format.

NoSQL vs SQL

If you're coming from a SQL background, here's how DynamoDB concepts map to what you know:

SQL Concept	DynamoDB Concept	Description
Database	Account/Region	All tables exist within your AWS account
Table	Table	Collection of items (same concept)
Row	Item	A single record in the table
Column	Attribute	A piece of data within an item
Primary Key	Partition Key (+ Sort Key)	Unique identifier for items
Index	Secondary Index (GSI/LSI)	Alternative ways to query data

Key Concepts

Partition Key

Every DynamoDB table requires a partition key (also called hash key). This is used to distribute data across partitions for scalability.

// Simple primary key: just partition key
{
  "userId": "user123",  // Partition key
  "email": "user@example.com",
  "name": "John Doe"
}

Sort Key

Optionally, you can add a sort key (also called range key) to create a composite primary key. This allows multiple items with the same partition key, sorted by the sort key.

// Composite primary key: partition key + sort key
{
  "userId": "user123",           // Partition key
  "todoId": "todo-001",          // Sort key
  "content": "Buy groceries",
  "completed": false
}

Secondary Indexes

DynamoDB only allows efficient queries on the primary key by default. Secondary indexes let you query on other attributes:

• Global Secondary Index (GSI): Query on any attribute, can have different partition/sort key than table
• Local Secondary Index (LSI): Same partition key as table, different sort key (must be defined at table creation)

How Amplify Uses DynamoDB

When you define a data model in Amplify Gen 2, here's what happens behind the scenes:

1. Amplify reads your model definition from amplify/data/resource.ts
2. AWS CDK generates CloudFormation templates
3. DynamoDB tables are created with appropriate keys and indexes
4. AWS AppSync GraphQL API is generated for CRUD operations
5. TypeScript types are generated for type-safe client operations

DynamoDB Pricing

DynamoDB has two pricing modes:

Mode	Best For	How It Works
On-Demand	Variable/unpredictable traffic	Pay per request, no capacity planning
Provisioned	Predictable traffic	Specify read/write capacity, lower cost at scale

By default, Amplify uses On-Demand mode, which is perfect for development and applications with variable traffic.

Data Access Patterns

With DynamoDB, it's important to think about how you'll access your data upfront. Common patterns include:

• Get by ID: Fetch a single item by its primary key (fastest)
• Query by partition key: Get all items with the same partition key
• Query with filter: Query plus filter on non-key attributes
• Scan: Read all items (expensive, avoid if possible)

Summary

• DynamoDB is a fully managed, serverless NoSQL database
• It uses partition keys and optional sort keys for organizing data
• Secondary indexes enable queries on non-key attributes
• Amplify abstracts most DynamoDB complexity through code-first models
• On-demand pricing with a generous free tier makes it cost-effective