Local Secondary Index

Local Secondary Index Overview

At its core, local secondary index is about doing one thing well inside your DynamoDB project. Once you understand the pattern, you can apply it consistently across features and teams.

Good local secondary index pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

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.

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

Amazon DynamoDB Cheatsheet

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

How Local Secondary Index Works in DynamoDB

Local 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 Local Secondary Index

In production, local 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

• Copying local secondary index snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up local secondary index.
• Leaving local secondary index untested, so regressions slip into production.
• Over-engineering local secondary index before you actually need the extra flexibility.

Key Takeaways

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