Pagination with SDK in DynamoDB - Step-by-Step Execution

Concept Flow - Pagination with SDK

Start Query

↓

Fetch First Page

↓

Check for LastEvaluatedKey

↓

Store LastEvaluatedKey

↓

Use LastEvaluatedKey to Fetch Next Page

↩Back to Check for LastEvaluatedKey

The SDK fetches data page by page. After each fetch, it checks if more data exists using LastEvaluatedKey. If yes, it uses that key to get the next page.

Execution Sample

DynamoDB

const params = {
  TableName: 'Users',
  Limit: 2
};

const data = await dynamodb.scan(params);
// Use data.LastEvaluatedKey for next page

This code fetches the first 2 items from the 'Users' table and prepares to fetch the next page if available.

Execution Table

Step	Action	Parameters	Result	Next Step
1	Call scan with Limit=2, no ExclusiveStartKey	{TableName:'Users', Limit:2}	Returns 2 items, LastEvaluatedKey present	Check LastEvaluatedKey
2	LastEvaluatedKey exists?	LastEvaluatedKey != null	Yes	Prepare next scan with ExclusiveStartKey
3	Call scan with Limit=2, ExclusiveStartKey=LastEvaluatedKey	{TableName:'Users', Limit:2, ExclusiveStartKey: key}	Returns next 2 items, LastEvaluatedKey present	Check LastEvaluatedKey
4	LastEvaluatedKey exists?	LastEvaluatedKey != null	Yes	Prepare next scan with ExclusiveStartKey
5	Call scan with Limit=2, ExclusiveStartKey=LastEvaluatedKey	{TableName:'Users', Limit:2, ExclusiveStartKey: key}	Returns last items, no LastEvaluatedKey	End Pagination
6	LastEvaluatedKey exists?	LastEvaluatedKey == null	No	Stop fetching pages

💡 No LastEvaluatedKey means all pages fetched; pagination ends.

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	Final
LastEvaluatedKey	null	key1	key2	null	null
FetchedItemsCount	0	2	4	6	6

Key Moments - 2 Insights

Why do we need LastEvaluatedKey to fetch the next page?

LastEvaluatedKey tells us where the last fetch stopped. Without it, we can't continue from the right place. See execution_table rows 2 and 4 where we check for it.

What happens if LastEvaluatedKey is null after a scan?

It means there are no more pages to fetch. The pagination ends. This is shown in execution_table row 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of LastEvaluatedKey after Step 3?

A key2

B key1

C null

D undefined

💡 Hint

Check variable_tracker column 'After Step 3' for LastEvaluatedKey value.

At which step does the pagination end according to the execution_table?

A Step 4

B Step 5

C Step 6

D Step 2

💡 Hint

Look for the step where LastEvaluatedKey is null and pagination stops.

If we increase Limit to 3, how would the FetchedItemsCount change after Step 1?

A It would be 2

B It would be 3

C It would be 6

D It would be 0

💡 Hint

Limit controls how many items are fetched per scan, see execution_sample and variable_tracker.

Concept Snapshot

Pagination with SDK:
- Use Limit to set page size.
- After each fetch, check LastEvaluatedKey.
- If present, use it as ExclusiveStartKey for next fetch.
- Repeat until LastEvaluatedKey is null.
- This fetches data page by page efficiently.

Full Transcript

Pagination with SDK in DynamoDB works by fetching data in pages. We start by calling scan with a Limit to get a small set of items. The response may include LastEvaluatedKey, which marks where to continue next. If LastEvaluatedKey exists, we use it as ExclusiveStartKey in the next scan call to get the next page. This repeats until LastEvaluatedKey is null, meaning no more data. The execution table shows each step: fetching pages, checking keys, and stopping. Variables like LastEvaluatedKey and FetchedItemsCount track progress. This method helps handle large data sets without loading all at once.