Scan pagination in DynamoDB - Step-by-Step Execution

Concept Flow - Scan pagination

Start Scan

↓

Fetch Page of Items

↓

Check for LastEvaluatedKey

Yes No↓

Save LastEvaluatedKey

↓

Use LastEvaluatedKey to Fetch Next Page

↓

Fetch Page of Items

Scan reads items page by page. If more items exist, it returns a LastEvaluatedKey to fetch the next page.

Execution Sample

DynamoDB

response = table.scan(Limit=2)
items = response['Items']
last_key = response.get('LastEvaluatedKey')
if last_key:
  response = table.scan(Limit=2, ExclusiveStartKey=last_key)

Scan DynamoDB table with a limit of 2 items per page, then fetch next page if more items exist.

Execution Table

Step	Action	Items Fetched	LastEvaluatedKey Present?	Next Step
1	Scan with Limit=2, no start key	Item1, Item2	Yes	Save LastEvaluatedKey, fetch next page
2	Scan with Limit=2, ExclusiveStartKey=last_key	Item3, Item4	Yes	Save LastEvaluatedKey, fetch next page
3	Scan with Limit=2, ExclusiveStartKey=last_key	Item5	No	End scan, no more pages

💡 No LastEvaluatedKey returned at step 3, scan completed all items.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
items	[]	[Item1, Item2]	[Item1, Item2, Item3, Item4]	[Item1, Item2, Item3, Item4, Item5]
last_key	null	key after step 1	key after step 2	null

Key Moments - 2 Insights

Why do we need to check for LastEvaluatedKey after each scan?

Because LastEvaluatedKey tells us if there are more items to fetch. Without it, we don't know if the scan is complete (see execution_table rows 1 and 2).

What happens if we don't use ExclusiveStartKey for the next scan?

The scan will start from the beginning again, causing repeated items and an infinite loop (refer to concept_flow loop back).

Visual Quiz - 3 Questions

Look at the execution_table, what items are fetched at step 2?

A Item3, Item4

B Item1, Item2

C Item5

D No items

💡 Hint

Check the 'Items Fetched' column in execution_table row 2.

At which step does the scan end because no LastEvaluatedKey is returned?

A Step 2

B Step 3

C Step 1

D Scan never ends

💡 Hint

Look at the 'LastEvaluatedKey Present?' column in execution_table.

If the Limit is increased to 5, how would the execution_table change?

A More steps with fewer items per step

B Same number of steps and items

C Fewer steps with more items per step

D Scan would not return LastEvaluatedKey

💡 Hint

Increasing Limit fetches more items per scan, reducing total steps (see concept_flow).

Concept Snapshot

Scan pagination in DynamoDB:
- Scan returns items in pages limited by 'Limit'.
- If more items exist, 'LastEvaluatedKey' is returned.
- Use 'ExclusiveStartKey' with LastEvaluatedKey to fetch next page.
- Repeat until no LastEvaluatedKey is returned.
- Prevents loading all items at once, useful for large tables.

Full Transcript

Scan pagination in DynamoDB works by fetching items in small pages. Each scan request returns a limited number of items and may include a LastEvaluatedKey if more items remain. This key is used as ExclusiveStartKey in the next scan to continue from where the last scan ended. This process repeats until no LastEvaluatedKey is returned, indicating all items have been scanned. This method helps manage large datasets efficiently by loading data in chunks.