Scan vs query performance in AWS - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Scan vs Query in DynamoDB

Which statement best describes the performance difference between a Scan and a Query operation in DynamoDB?

A Both Scan and Query read all items but Query is slower due to filtering.

B Scan reads items based on primary key and is faster; Query reads all items and is slower.

C Scan reads all items in a table and is slower; Query reads items based on primary key and is faster.

D Scan and Query have identical performance because they both use indexes.

💡 Hint

Think about how many items each operation reads from the table.

Scan reads every item in the table, which makes it slower and more resource-intensive. Query uses the primary key to find specific items, making it faster and more efficient.

❓ service_behavior

intermediate

Result Count Differences Between Scan and Query

You perform a Scan and a Query on a DynamoDB table with 1000 items. The Query uses a partition key that matches 50 items. How many items will each operation read?

A Scan reads 1000 items; Query reads 50 items.

B Scan reads 50 items; Query reads 1000 items.

C Both Scan and Query read 1000 items.

D Both Scan and Query read 50 items.

💡 Hint

Consider what each operation scans or queries in the table.

Scan reads all 1000 items regardless of filter. Query reads only the 50 items matching the partition key.

❓ Architecture

advanced

Optimizing DynamoDB Access Patterns

You want to design a DynamoDB table to minimize the use of Scan operations for better performance. Which design choice helps achieve this?

A Use a well-defined partition key and sort key to enable efficient Query operations.

B Avoid using any keys and rely on Scan for all data retrieval.

C Use only Scan operations with filters to reduce data read.

D Store all data in a single partition to simplify access.

💡 Hint

Think about how keys help DynamoDB find data quickly.

Using partition and sort keys allows Query operations to efficiently retrieve data without scanning the entire table, improving performance.

❓ security

advanced

Security Implications of Scan vs Query

Which security risk is higher when using Scan operations compared to Query operations in DynamoDB?

A Scan operations are encrypted by default, Query operations are not.

B Scan may expose more data than intended because it reads the entire table.

C Query exposes more data because it uses keys.

D There is no difference in security risks between Scan and Query.

💡 Hint

Consider how much data each operation accesses.

Scan reads all items, which can expose more data if permissions are not tightly controlled. Query limits data access to specific keys, reducing exposure.

✅ Best Practice

expert

Choosing Between Scan and Query for Large Tables

You manage a DynamoDB table with millions of items. You need to retrieve items matching a specific attribute that is not part of the primary key. Which approach is best to maintain performance?

A Use Scan with a filter expression on the attribute to find matching items.

B Export the table data and search externally to avoid Scan or Query.

C Add the attribute to the primary key and use Query on the main table.

D Create a Global Secondary Index (GSI) on that attribute and use Query on the GSI.

💡 Hint

Think about how to query non-key attributes efficiently.

Creating a GSI allows Query operations on non-key attributes efficiently, avoiding costly Scan operations on large tables.