Pagination with SDK in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is pagination in the context of DynamoDB SDK?

Pagination means fetching data in small parts or pages instead of all at once. It helps handle large data sets efficiently and avoids timeouts or memory issues.

beginner

Which DynamoDB SDK method helps you continue fetching the next page of results?

The method uses a special value called LastEvaluatedKey. You pass this key as ExclusiveStartKey in the next request to get the next page.

beginner

Why should you avoid fetching all items in one request in DynamoDB?

Fetching all items at once can cause slow responses, timeouts, or memory overload. Pagination breaks data into smaller chunks for faster and safer processing.

beginner

How do you know when you have reached the last page of results in DynamoDB pagination?

When the response does NOT include LastEvaluatedKey, it means there are no more pages to fetch. You have reached the end of the data.

beginner

What parameter controls how many items DynamoDB returns per page?

The Limit parameter sets the maximum number of items returned in one page. You can adjust it to control page size.

In DynamoDB SDK, which key do you use to fetch the next page of results?

A NextPageToken

B LastEvaluatedKey

C StartKey

D PageNumber

DynamoDB returns LastEvaluatedKey in the response to indicate where to start the next page.

What happens if you do not use pagination and request all items at once?

A DynamoDB automatically paginates for you

B You get all data instantly without issues

C You might get timeouts or memory problems

D The query will fail immediately

Fetching too much data at once can cause timeouts or memory overload.

Which parameter do you set to limit the number of items returned per page?

A Limit

B PageSize

C MaxItems

D Count

The Limit parameter controls how many items DynamoDB returns in one request.

How do you know you have reached the last page of results?

A Response includes LastEvaluatedKey

B Response includes NextPageToken

C Response includes PageNumber

D Response does not include LastEvaluatedKey

No LastEvaluatedKey means no more pages to fetch.

What do you pass as ExclusiveStartKey in the next request?

A The LastEvaluatedKey from previous response

B The total count of items

C A random key

D The first item key from previous page

You pass LastEvaluatedKey as ExclusiveStartKey to continue from where you left off.

Explain how pagination works in DynamoDB SDK and why it is important.

Think about how you read a book page by page instead of all at once.

Describe the steps to fetch multiple pages of data using DynamoDB SDK.

Imagine turning pages until you reach the last one.

Practice

1. What does the Limit parameter do when paginating results in DynamoDB SDK?

easy

A. It specifies the starting point for the next page.

B. It sets the maximum number of items returned in one page.

C. It filters items based on a condition.

D. It sorts the results in ascending order.

Solution

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

   The Limit parameter controls how many items DynamoDB returns in a single request, effectively setting the page size.

2. Step 2: Differentiate from other parameters

   ExclusiveStartKey sets the starting point for the next page, not Limit. Filtering and sorting are handled differently.

3. Final Answer:

   It sets the maximum number of items returned in one page. -> Option B

4. Quick Check:

   Limit = page size [OK]

Hint: Limit controls page size, not start or filter [OK]

Common Mistakes:

• Confusing Limit with ExclusiveStartKey
• Thinking Limit filters data
• Assuming Limit sorts results

2. Which of the following is the correct way to continue fetching the next page of results in DynamoDB SDK?

easy

A. Set StartKey to zero.

B. Use Limit with the last item key.

C. Set ExclusiveStartKey to the last evaluated key from previous response.

D. Use NextPageToken parameter.

Solution

1. Step 1: Identify the parameter for pagination continuation

   DynamoDB uses ExclusiveStartKey to tell the query where to start for the next page.

2. Step 2: Verify other options

   Limit sets page size, StartKey is not a valid parameter, and NextPageToken is not used in DynamoDB SDK.

3. Final Answer:

   Set ExclusiveStartKey to the last evaluated key from previous response. -> Option C

4. Quick Check:

   Use ExclusiveStartKey for next page [OK]

Hint: Use ExclusiveStartKey to continue pagination [OK]

Common Mistakes:

• Using Limit to continue pages
• Using invalid parameter StartKey
• Assuming NextPageToken exists in DynamoDB

3. Given the following DynamoDB SDK code snippet, what will be the output if LastEvaluatedKey is not empty?

const params = { TableName: 'Books', Limit: 2 };
const data = await dynamoDbClient.scan(params);
console.log(data.Items.length);
console.log(data.LastEvaluatedKey !== undefined);

medium

A. Error due to missing ExclusiveStartKey

B. All items and false

C. 2 and false

D. 2 and true

Solution

1. Step 1: Understand Limit effect on Items returned

   With Limit: 2, the scan returns at most 2 items, so data.Items.length will be 2.

2. Step 2: Check LastEvaluatedKey presence

   If LastEvaluatedKey is not empty, it means more pages exist, so data.LastEvaluatedKey !== undefined is true.

3. Final Answer:

   2 and true -> Option D

4. Quick Check:

   Limit = 2 items, LastEvaluatedKey present = true [OK]

Hint: Limit caps items; LastEvaluatedKey true means more pages [OK]

Common Mistakes:

• Assuming all items returned ignoring Limit
• Thinking LastEvaluatedKey is false when present
• Expecting error without ExclusiveStartKey

4. You wrote this code to paginate DynamoDB scan results but it returns only the first page repeatedly:

let params = { TableName: 'Users', Limit: 3 };
let data;
do {
  data = await dynamoDbClient.scan(params);
  console.log(data.Items);
} while (data.LastEvaluatedKey);

What is the main issue?

medium

A. Missing update of ExclusiveStartKey in params inside the loop.

B. Limit should be increased to fetch all items.

C. The loop condition should check data.Items instead.

D. The scan method does not support pagination.

Solution

1. Step 1: Analyze loop behavior

   The code calls scan repeatedly but never updates ExclusiveStartKey, so it fetches the same first page each time.

2. Step 2: Identify correct fix

   To get next pages, params.ExclusiveStartKey must be set to data.LastEvaluatedKey inside the loop.

3. Final Answer:

   Missing update of ExclusiveStartKey in params inside the loop. -> Option A

4. Quick Check:

   Update ExclusiveStartKey to paginate [OK]

Hint: Update ExclusiveStartKey each loop to get next page [OK]

Common Mistakes:

• Not updating ExclusiveStartKey inside loop
• Increasing Limit instead of paginating
• Wrong loop condition on Items
• Thinking scan can't paginate

5. You want to fetch all items from a large DynamoDB table using pagination with the SDK. Which approach correctly handles this scenario?

hard

A. Use a loop that calls scan with Limit, updating ExclusiveStartKey each time until LastEvaluatedKey is undefined.

B. Call scan once with a very large Limit to get all items at once.

C. Use scan without Limit and stop when Items array is empty.

D. Call scan repeatedly without ExclusiveStartKey until Items length is zero.

Solution

1. Step 1: Understand DynamoDB pagination for large tables

   Large tables require multiple scan calls with a Limit to avoid timeouts and memory issues.

2. Step 2: Correctly implement pagination loop

   Each scan call should use ExclusiveStartKey from the previous LastEvaluatedKey until it is undefined, indicating no more pages.

3. Final Answer:

   Use a loop that calls scan with Limit, updating ExclusiveStartKey each time until LastEvaluatedKey is undefined. -> Option A

4. Quick Check:

   Loop with Limit and ExclusiveStartKey until done [OK]

Hint: Loop with Limit and ExclusiveStartKey until no LastEvaluatedKey [OK]

Common Mistakes:

• Using huge Limit causing timeouts
• Ignoring ExclusiveStartKey for next pages
• Stopping on empty Items instead of LastEvaluatedKey
• Calling scan repeatedly without pagination