Local Secondary Index

What is a Local Secondary Index (LSI)?

It’s an index we define that shares the table’s partition key but uses an alternate sort key for scans and queries. It must be created at table creation time you cannot add, remove, or modify it later. All queries based on that sort key are significantly faster using the index than the main table.

AWS Developer

AWS Developer: Local Secondary Indexes (LSIs)

DynamoDB: Scan vs Query

Choose an operation below and interact with the data to see exactly what DynamoDB searches and returns.

Scan the Users table

A Scan looks through the table. Optionally choose a value to filter the results.

Filter by Email No filter — return everything alice@example.com bob@example.com john@example.com

DynamoDB scans:

Users → Every item → Filter → Results

DynamoDB operation

Returned data

Build a Query

Pick a partition key and sort key value. DynamoDB will use those values to find the matching item.

Query this:

Partition Key

UserId

AND

Sort Key

CreatedAt

1

Find the partition

UserId =

2

Use the sort key

CreatedAt =

✓

Return the matching item

DynamoDB returns the item shown below.

DynamoDB Query

Returned data

Users Table

The base DynamoDB table

Base Table

UserId Partition Key	CreatedAt Sort Key	Email	Name
user-123	2026-09-01	alice@example.com	Alice
user-456	2026-09-05	bob@example.com	Bob
user-789	2026-09-10	john@example.com	John

EmailIndex

Same partition key, different sort key

Local Secondary Index

UserId Partition Key	Email LSI Sort Key
user-123	alice@example.com
user-456	bob@example.com
user-789	john@example.com

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