Global Secondary Index (GSI) concept in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the purpose of a Global Secondary Index

What is the main purpose of creating a Global Secondary Index (GSI) in DynamoDB?

A To allow querying the table using an alternate key with different partition and sort keys

B To increase the storage capacity of the main table automatically

C To create a backup of the table data in another region

D To enforce stricter data validation rules on the main table

💡 Hint

Think about why you might want to search your data in a different way than the main key.

A Global Secondary Index lets you query your DynamoDB table using a different partition key and optional sort key than the main table. This helps when you want to find items based on attributes other than the primary key.

❓ query_result

intermediate

Querying with a Global Secondary Index

Given a DynamoDB table Orders with a GSI named CustomerIndex that uses CustomerID as the partition key, what will the following query return?

Query on CustomerIndex where CustomerID = 'C123'

A All orders placed by customer with ID 'C123'

B All orders sorted by order date for all customers

C All orders with order ID 'C123'

D An error because <code>CustomerID</code> is not the primary key of the main table

💡 Hint

Remember that a GSI lets you query by the alternate key defined in the index.

The query on the GSI using CustomerID = 'C123' returns all items where the CustomerID attribute matches 'C123'. This means all orders placed by that customer.

📝 Syntax

advanced

Identifying correct GSI creation syntax

Which of the following JSON snippets correctly defines a Global Secondary Index named GSI1 with Category as the partition key and Price as the sort key?

A { "IndexName": "GSI1", "KeySchema": [{"AttributeName": "Category", "KeyType": "RANGE"}, {"AttributeName": "Price", "KeyType": "HASH"}], "Projection": {"ProjectionType": "KEYS_ONLY"} }

B { "IndexName": "GSI1", "KeySchema": [{"AttributeName": "Price", "KeyType": "HASH"}, {"AttributeName": "Category", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"} }

C { "IndexName": "GSI1", "KeySchema": [{"AttributeName": "Category", "KeyType": "HASH"}, {"AttributeName": "Price", "KeyType": "RANGE"}], "Projection": {"ProjectionType": "ALL"} }

D { "IndexName": "GSI1", "KeySchema": [{"AttributeName": "Category"}], "Projection": {"ProjectionType": "ALL"} }

💡 Hint

The partition key must have KeyType as HASH and the sort key as RANGE.

Option C correctly sets Category as the partition key (HASH) and Price as the sort key (RANGE). The projection type ALL means all attributes are projected.

❓ optimization

advanced

Choosing attributes to project in a GSI

You want to optimize read performance and reduce storage costs for a GSI that queries only OrderID and OrderDate. Which projection type should you choose?

A NONE - no attributes are projected

B KEYS_ONLY - projects only the index keys

C ALL - projects all attributes from the main table

D INCLUDE - projects only <code>OrderID</code> and <code>OrderDate</code>

💡 Hint

Think about projecting only the attributes you need to reduce storage and improve query speed.

The INCLUDE projection type lets you specify only the attributes you want in the index, reducing storage and improving read efficiency when you only need specific fields.

🔧 Debug

expert

Diagnosing a GSI query error

You run a query on a GSI named GSI2 with partition key UserID, but get the error: ValidationException: Query condition missed key schema element: UserID. What is the most likely cause?

A The GSI <code>GSI2</code> does not exist on the table

B The query did not specify the <code>UserID</code> value in the key condition expression

C The main table does not have a <code>UserID</code> attribute

D The query used the main table's primary key instead of the GSI

💡 Hint

Check if the query includes the partition key value required by the index.

The error means the query did not include the required partition key UserID in the key condition. Every query on a GSI must specify the partition key value.