Module 3: DynamoDB Table Design

Introduction to DynamoDB

Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability. DynamoDB lets you offload the administrative burdens of operating and scaling a distributed database so that you don't have to worry about hardware provisioning, setup and configuration, replication, software patching, or cluster scaling.

With DynamoDB, you can create database tables that can store and retrieve any amount of data and serve any level of request traffic. You can scale up or scale down your tables' throughput capacity without downtime or performance degradation.

Key Differences from Relational Databases

If you're familiar with relational databases like MySQL or PostgreSQL, you'll need to adjust your thinking when working with DynamoDB:

• Schema-less: DynamoDB is schema-less, meaning each item in a table can have different attributes
• Access patterns: You design your tables based on how you'll access the data, not how you'll store it
• No joins: DynamoDB doesn't support joins like relational databases do
• Single-digit millisecond performance: DynamoDB is designed for extremely fast reads and writes

DynamoDB Core Concepts

Tables, Items, and Attributes

The basic DynamoDB components are:

• Tables: Similar to tables in other databases, a DynamoDB table is a collection of data
• Items: Each table contains multiple items. An item is similar to a row or record in other databases
• Attributes: Each item is composed of one or more attributes. An attribute is a fundamental data element that needs no further decomposition

Primary Keys

When you create a table, you must specify its primary key. The primary key uniquely identifies each item in the table, so that no two items can have the same key. DynamoDB supports two types of primary keys:

• Partition key: A simple primary key, composed of one attribute. DynamoDB uses the partition key's value as input to an internal hash function. The output from the hash function determines the partition where the item will be stored.
• Partition key and sort key: A composite primary key, composed of two attributes. The first attribute is the partition key, and the second attribute is the sort key. All items with the same partition key are stored together, in sorted order by sort key value.

Understanding Partitions

DynamoDB stores data in partitions. A partition is an allocation of storage for a table, backed by solid-state drives (SSDs) and automatically replicated across multiple Availability Zones within an AWS Region. Partition management is handled entirely by DynamoDB—you never have to manage partitions yourself.

When you create a table, DynamoDB allocates enough partitions to handle your provisioned throughput requirements. As your application data and throughput requirements change, DynamoDB automatically adjusts by splitting busy partitions and distributing the data over a larger number of partitions.

// Example CloudFormation template for a DynamoDB table
{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "UsersTable": {
      "Type": "AWS::DynamoDB::Table",
      "Properties": {
        "TableName": "Users",
        "BillingMode": "PAY_PER_REQUEST",
        "AttributeDefinitions": [
          {
            "AttributeName": "userId",
            "AttributeType": "S"
          },
          {
            "AttributeName": "email",
            "AttributeType": "S"
          }
        ],
        "KeySchema": [
          {
            "AttributeName": "userId",
            "KeyType": "HASH"
          }
        ],
        "GlobalSecondaryIndexes": [
          {
            "IndexName": "EmailIndex",
            "KeySchema": [
              {
                "AttributeName": "email",
                "KeyType": "HASH"
              }
            ],
            "Projection": {
              "ProjectionType": "ALL"
            }
          }
        ]
      }
    }
  }
}

DynamoDB Table Design Best Practices

Effective Partition Key Design

The partition key is used to determine the physical partition where the item will be stored. A well-designed partition key will:

• Distribute data evenly across partitions
• Avoid "hot spots" in your database
• Support your most common access patterns

Good candidates for partition keys include:

• User ID (when data is being accessed primarily by user)
• Item ID or order ID (for unique items)
• Session ID (for session data)
• Device ID (for IoT applications)

Poor candidates for partition keys include:

• Status codes (limited cardinality leads to hot partitions)
• Date/timestamps (can create temporal hot partitions)
• Boolean values (only two possible values)

Using Composite Keys Effectively

A composite key (partition key + sort key) allows you to:

• Store multiple items with the same partition key
• Organize related data together
• Perform efficient range queries on the sort key

Common patterns include:

• One-to-many relationships: Use the "one" as the partition key and identifiers for the "many" as sort keys
• Time-series data: Use an entity ID as the partition key and timestamps as the sort key
• Hierarchical data: Use parent ID as partition key and child ID as sort key

Design for Access Patterns

Unlike relational databases where you can add indexes later, with DynamoDB you need to identify your access patterns upfront and design your tables accordingly:

• Identify all the ways your application will need to access the data
• Design your primary key and any secondary indexes to support these access patterns
• Consider denormalizing your data to optimize for query performance

// Example of DynamoDB table design for a social media app
// Primary table: UserId (partition) and ItemType#Timestamp (sort)

// Example items in the table:
// User profile:
{
  "UserId": "U123",
  "ItemType": "PROFILE",
  "Name": "John Doe",
  "Email": "john@example.com"
}

// User post:
{
  "UserId": "U123",
  "ItemType": "POST#2023-06-15T14:30:00Z",
  "Content": "Hello world!",
  "Likes": 42
}

// User follower:
{
  "UserId": "U123",
  "ItemType": "FOLLOWER#U456",
  "FollowerName": "Jane Smith"
}

Key Topics

Guided Project

In the guided project for this module, you'll apply what you've learned about DynamoDB table design to create the database tables for your Learn and Be Curious project.

Project: Creating DynamoDB Tables for Your Application

This project will guide you through designing and creating DynamoDB tables based on the API you designed in Module 2.

Additional Resources