When Scan is acceptable in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

When is using Scan in DynamoDB acceptable?

Which situation is the best reason to use a Scan operation in DynamoDB?

A When you want to query items using a specific partition key.

B When you want to get a single item by its primary key.

C When you need to retrieve all items from a small table without filters.

D When you want to update an item conditionally.

💡 Hint

Think about when scanning the whole table is not costly or inefficient.

Scan reads every item in the table, so it is acceptable only when the table is small and you need all data without filtering by keys.

🧠 Conceptual

intermediate

Why avoid Scan on large DynamoDB tables?

What is the main reason to avoid using Scan on large DynamoDB tables?

A Scan does not support filtering items.

B Scan can cause high latency and consume a lot of read capacity units.

C Scan only returns items sorted by primary key.

D Scan cannot read all attributes of an item.

💡 Hint

Think about the cost and speed of reading many items.

Scan reads every item, which can be slow and expensive on large tables because it consumes many read capacity units and increases latency.

❓ query_result

advanced

Output of Scan on a small DynamoDB table

Given a DynamoDB table with 3 items, what will be the output of a Scan operation without filters?

DynamoDB

Table items:
1. {"id": "1", "name": "Alice"}
2. {"id": "2", "name": "Bob"}
3. {"id": "3", "name": "Carol"}

Scan operation: scan the whole table without any filter.

A SyntaxError

B [{"id": "1", "name": "Alice"}]

C []

D [{"id": "1", "name": "Alice"}, {"id": "2", "name": "Bob"}, {"id": "3", "name": "Carol"}]

💡 Hint

Scan returns all items if no filter is applied.

Scan reads all items in the table and returns them as a list when no filter is used.

❓ schema

advanced

Design choice for Scan usage

You have a DynamoDB table expected to grow very large. You need to occasionally retrieve all items for a report. What is the best design choice to allow efficient Scan usage?

A Keep the table small by archiving old data to another storage regularly.

B Use Scan frequently on the large table without changes.

C Use Query with a random partition key to simulate Scan.

D Avoid any data retrieval to prevent Scan.

💡 Hint

Think about how to keep Scan efficient by controlling table size.

Archiving old data keeps the table small, making Scan efficient and acceptable for occasional full reads.

🔧 Debug

expert

Why does this Scan operation cause high latency?

You run a Scan on a large DynamoDB table and notice very high latency and throttling. Which option explains the cause?

DynamoDB

Scan operation without any filter or pagination on a table with millions of items.

A Scan reads the entire table at once, consuming too many read capacity units and causing throttling.

B Scan only reads items with a specific partition key, so it should be fast.

C Scan automatically uses indexes to speed up reading, so latency is unrelated.

D Scan only reads the first 100 items, so latency should be low.

💡 Hint

Consider how Scan works internally on large tables.

Scan reads every item in the table, so on large tables it consumes many read capacity units at once, causing throttling and high latency.