Limit and pagination in DynamoDB - Step-by-Step Execution

Concept Flow - Limit and pagination

Start Query

↓

Set Limit N

↓

Fetch up to N items

↓

Check if More Items

Yes No↓

Return Items

↓

Save LastEvaluatedKey

↓

Use LastEvaluatedKey for Next Query

The query fetches up to a set limit of items, checks if more items exist, and if so, saves a key to fetch the next page.

Execution Sample

DynamoDB

Query with Limit=3
Fetch first 3 items
Check LastEvaluatedKey
Use it for next page

This query fetches 3 items from a DynamoDB table and prepares for pagination if more items exist.

Execution Table

Step	Action	Limit	Items Fetched	LastEvaluatedKey	More Items?
1	Start Query	3	0	null	Yes
2	Fetch up to Limit	3	[Item1, Item2, Item3]	Key3	Yes
3	Return first page	3	[Item1, Item2, Item3]	Key3	Yes
4	Use LastEvaluatedKey for next query	3	0	Key3	Yes
5	Fetch next 3 items	3	[Item4, Item5]	null	No
6	Return second page	3	[Item4, Item5]	null	No
7	No more items, end pagination	3	N/A	null	No

💡 No more items to fetch, LastEvaluatedKey is null, pagination ends.

Variable Tracker

Variable	Start	After Step 2	After Step 5	Final
Limit	3	3	3	3
Items Fetched	[]	[Item1, Item2, Item3]	[Item4, Item5]	[Item4, Item5]
LastEvaluatedKey	null	Key3	null	null
More Items?	Yes	Yes	No	No

Key Moments - 3 Insights

Why does the query return fewer items than the limit on the second page?

Because the table has only 5 items total, the second fetch returns only 2 items. This is shown in execution_table row 5 where only 2 items are fetched even though the limit is 3.

What does LastEvaluatedKey represent and why is it important?

LastEvaluatedKey marks the last item fetched and is used to continue fetching the next page. In execution_table rows 2 and 4, it is saved and used to fetch the next set of items.

When does pagination stop?

Pagination stops when LastEvaluatedKey is null, meaning no more items to fetch. This is shown in execution_table row 7 where the process ends.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of LastEvaluatedKey after the first fetch?

A Key3

B null

C Key5

D Item3

💡 Hint

Check the 'LastEvaluatedKey' column in row 2 of the execution_table.

At which step does the query fetch fewer items than the limit?

A Step 2

B Step 5

C Step 3

D Step 6

💡 Hint

Look at the 'Items Fetched' column and compare with 'Limit' in the execution_table.

If the table had 10 items, how would the 'More Items?' value change after step 6?

A It would be 'No'

B It would be 'null'

C It would be 'Yes'

D It would be 'Key10'

💡 Hint

Refer to the 'More Items?' column and understand that more items exist if total items exceed fetched items.

Concept Snapshot

DynamoDB Limit and Pagination:
- Use Limit to fetch up to N items per query.
- If more items exist, LastEvaluatedKey is returned.
- Use LastEvaluatedKey in next query to get next page.
- Pagination ends when LastEvaluatedKey is null.
- Helps manage large datasets in small chunks.

Full Transcript

This visual execution shows how DynamoDB handles Limit and pagination. The query starts with a Limit of 3 items. It fetches the first 3 items and returns them with a LastEvaluatedKey indicating more items exist. Using this key, the next query fetches the next set of items. When fewer items than the limit are returned and LastEvaluatedKey is null, pagination ends. Variables like Limit, Items Fetched, LastEvaluatedKey, and More Items? change step-by-step to track progress. Key moments clarify why fewer items may be returned and how pagination stops. The quiz tests understanding of these steps and variable values.