Global Secondary Index

Global Secondary Index Overview

Global Secondary Index is a building block you will reach for often in DynamoDB. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn global secondary index properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real DynamoDB projects.

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient, QueryCommand } from '@aws-sdk/lib-dynamodb';

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

const { Items } = await docClient.send(new QueryCommand({
  TableName: 'Orders',
  KeyConditionExpression: 'pk = :pk AND begins_with(sk, :prefix)',
  ExpressionAttributeValues: { ':pk': 'USER#42', ':prefix': 'ORDER#' },
  Limit: 25,
}));

QueryCommand reads a partition efficiently using key conditions; add IndexName for a GSI.

Global Secondary Index Example

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocumentClient } from '@aws-sdk/lib-dynamodb';

const docClient = DynamoDBDocumentClient.from(new DynamoDBClient({}));
// docClient.send(new PutCommand(...)) etc.

• Start from a minimal Global Secondary Index example and grow it only as needed.
• Keep configuration explicit so Global Secondary Index behaves the same in every environment.
• Name things clearly so teammates understand your Global Secondary Index at a glance.
• Add tests around Global Secondary Index early to lock in expected behaviour.

Amazon DynamoDB Cheatsheet

Handy DynamoDB (AWS SDK v3) reference related to global secondary index.

How Global Secondary Index Works in DynamoDB

Global Secondary Index builds on DynamoDB's key-value and document model, where every item lives in a partition chosen by its partition key and is optionally ordered by a sort key.

QueryCommand reads a partition efficiently using key conditions; add IndexName for a GSI.

• Design access patterns first, then model keys around them.
• Prefer Query over Scan for predictable performance.
• Use expressions to read and write only what you need.
• Keep items small and avoid hot partitions.

Practical Guidance for Global Secondary Index

In production, global secondary index should be cost-aware and resilient. Right-size capacity, handle throttling with retries, and lean on indexes to support your query patterns.

Common Mistakes

• Skipping error handling and edge cases when wiring up global secondary index.
• Leaving global secondary index untested, so regressions slip into production.
• Over-engineering global secondary index before you actually need the extra flexibility.
• Ignoring documentation, which makes global secondary index hard for the next developer to change.

Key Takeaways

• Global Secondary Index is a core part of working effectively with DynamoDB.
• Start small and keep global secondary index focused on a single responsibility.
• Apply consistent patterns so global secondary index scales across your project.
• Test and document global secondary index to keep it maintainable over time.