Limit and pagination in DynamoDB

Introduction

Limit and pagination help you get data in small parts instead of all at once. This makes it easier to handle and faster to load.

When you want to show only 10 items per page in a shopping app.

When you have a big list of users and want to load them bit by bit.

When you want to save data transfer by not loading everything at once.

When you want to let users scroll through data without waiting long.

When you want to avoid timeouts by fetching data in smaller chunks.

Syntax

DynamoDB

Scan or Query operation with parameters:
{
  Limit: number,
  ExclusiveStartKey: { primaryKeyAttribute: value, ... } (optional)
}

Limit sets the max number of items to return.

ExclusiveStartKey tells DynamoDB where to continue from for the next page.

Examples

Get up to 5 items from the Products table.

DynamoDB

Scan({
  TableName: 'Products',
  Limit: 5
})

Get up to 10 orders for customer 123.

DynamoDB

Query({
  TableName: 'Orders',
  KeyConditionExpression: 'CustomerId = :cid',
  ExpressionAttributeValues: { ':cid': '123' },
  Limit: 10
})

Get next 5 items starting after ProductId 'P100'.

DynamoDB

Scan({
  TableName: 'Products',
  Limit: 5,
  ExclusiveStartKey: { ProductId: 'P100' }
})

Sample Program

This example fetches the first 3 items from the 'Books' table, then fetches the next 3 items using pagination.

DynamoDB

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB.DocumentClient();

async function fetchFirstPage() {
  const params = {
    TableName: 'Books',
    Limit: 3
  };
  const data = await dynamodb.scan(params).promise();
  console.log('First page items:', data.Items);
  return data.LastEvaluatedKey;
}

async function fetchNextPage(lastKey) {
  if (!lastKey) {
    console.log('No more pages');
    return;
  }
  const params = {
    TableName: 'Books',
    Limit: 3,
    ExclusiveStartKey: lastKey
  };
  const data = await dynamodb.scan(params).promise();
  console.log('Next page items:', data.Items);
  return data.LastEvaluatedKey;
}

(async () => {
  const lastKey = await fetchFirstPage();
  await fetchNextPage(lastKey);
})();

Important Notes

If LastEvaluatedKey is empty, you reached the last page.

Limit is a maximum, DynamoDB may return fewer items.

Use ExclusiveStartKey from last response to get the next page.

Summary

Limit controls how many items you get at once.

Pagination uses ExclusiveStartKey to continue from last place.

This helps handle large data smoothly and fast.

Practice

1. What does the Limit parameter do in a DynamoDB query or scan?

easy

A. It filters items based on a condition.

B. It sets the maximum size of each item returned.

C. It limits the number of items returned in one response.

D. It sorts the items in ascending order.

Solution

1. Step 1: Understand the role of Limit in DynamoDB

   The Limit parameter controls how many items DynamoDB returns in a single query or scan response.

2. Step 2: Differentiate Limit from other parameters

   Limit does not filter or sort items; it only restricts the count of items returned at once.

3. Final Answer:

   It limits the number of items returned in one response. -> Option C

4. Quick Check:

   Limit = number of items returned [OK]

Hint: Limit sets max items per response, not filtering or sorting [OK]

Common Mistakes:

• Confusing Limit with filtering conditions
• Thinking Limit sorts the results
• Assuming Limit changes item size

2. Which of the following is the correct way to specify a limit of 5 items in a DynamoDB query using AWS SDK for JavaScript?

easy

A. query({ TableName: 'MyTable', MaxResults: 5 })

B. query({ TableName: 'MyTable', Limit: 5 })

C. query({ TableName: 'MyTable', MaxItems: 5 })

D. query({ TableName: 'MyTable', limit: 5 })

Solution

1. Step 1: Check parameter case sensitivity in AWS SDK

   In AWS SDK for JavaScript, parameter names are case-sensitive and 'Limit' must be capitalized.

2. Step 2: Verify correct parameter name for limiting items

   The correct parameter to limit items is 'Limit', not 'limit', 'MaxItems', or 'MaxResults'.

3. Final Answer:

   query({ TableName: 'MyTable', Limit: 5 }) -> Option B

4. Quick Check:

   Correct case and name for limit is 'Limit' [OK]

Hint: Use exact 'Limit' with capital L in query parameters [OK]

Common Mistakes:

• Using lowercase 'limit' instead of 'Limit'
• Using wrong parameter names like MaxItems
• Confusing limit with max results

3. Given a DynamoDB table with 10 items, what will be the result of this scan operation?

scan({ TableName: 'MyTable', Limit: 3 })

medium

A. Returns all 10 items in one response.

B. Returns exactly 3 items in the response.

C. Returns an error because Limit is too small.

D. Returns 3 items and a LastEvaluatedKey for next page.

Solution

1. Step 1: Understand Limit effect on scan results

   Limit restricts the number of items returned in one response to 3.

2. Step 2: Recognize pagination behavior with LastEvaluatedKey

   Since there are more items (10 total), DynamoDB returns 3 items plus a LastEvaluatedKey to continue scanning next items.

3. Final Answer:

   Returns 3 items and a LastEvaluatedKey for next page. -> Option D

4. Quick Check:

   Limit 3 + more items = partial results + LastEvaluatedKey [OK]

Hint: Limit returns partial items plus LastEvaluatedKey if more exist [OK]

Common Mistakes:

• Assuming all items return ignoring Limit
• Thinking Limit causes error if small
• Missing LastEvaluatedKey for pagination

4. You run this DynamoDB query but get an error:

query({ TableName: 'MyTable', Limit: 5, ExclusiveStartKey: { id: '123' } })

What is the most likely cause?

medium

A. ExclusiveStartKey is missing required key attributes.

B. Limit cannot be used with ExclusiveStartKey.

C. TableName is incorrect.

D. Limit value must be greater than 10.

Solution

1. Step 1: Understand ExclusiveStartKey requirements

   ExclusiveStartKey must include the full primary key attributes exactly as stored in the table.

2. Step 2: Identify error cause

   If the provided ExclusiveStartKey lacks required key attributes or has wrong format, DynamoDB returns an error.

3. Final Answer:

   ExclusiveStartKey is missing required key attributes. -> Option A

4. Quick Check:

   ExclusiveStartKey needs full primary key [OK]

Hint: ExclusiveStartKey must have full primary key attributes [OK]

Common Mistakes:

• Thinking Limit and ExclusiveStartKey cannot be combined
• Assuming TableName typo causes this error
• Believing Limit must be > 10

5. You want to fetch all items from a large DynamoDB table but only 4 items at a time to avoid timeouts. Which approach correctly implements pagination?

hard

A. Use Limit: 4 and pass LastEvaluatedKey from previous response as ExclusiveStartKey in next query.

B. Use Limit: 4 and always start query with ExclusiveStartKey: null.

C. Use Limit: 4 and increase Limit by 4 each time to get next items.

D. Use Limit: 4 and scan the whole table once without ExclusiveStartKey.

Solution

1. Step 1: Understand pagination with Limit and ExclusiveStartKey

   Limit controls how many items are returned per request. To get next items, use ExclusiveStartKey with LastEvaluatedKey from previous response.

2. Step 2: Confirm correct pagination process

   Use Limit: 4 and pass LastEvaluatedKey from previous response as ExclusiveStartKey in next query to fetch items in pages. Restarting from the beginning, increasing Limit, or scanning without pagination leads to repeated or incomplete results.

3. Final Answer:

   Use Limit: 4 and pass LastEvaluatedKey from previous response as ExclusiveStartKey in next query. -> Option A

4. Quick Check:

   Pagination = Limit + ExclusiveStartKey chaining [OK]

Hint: Pass LastEvaluatedKey as ExclusiveStartKey to paginate [OK]

Common Mistakes:

• Restarting query without ExclusiveStartKey
• Increasing Limit instead of paginating
• Scanning whole table ignoring pagination