Partition key and sort key in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Partition Key Uniqueness

In a DynamoDB table, what does the partition key uniquely identify?

A The timestamp when the item was created

B A unique item in the table regardless of sort key

C The order in which items are stored physically

D A group of items that share the same partition key value

💡 Hint

Think about how partition keys group data in DynamoDB.

The partition key groups items into partitions. Multiple items can share the same partition key but differ by sort key.

❓ Architecture

intermediate

Choosing Keys for Efficient Queries

You want to design a DynamoDB table to store customer orders. Each customer can have multiple orders. Which key design allows efficient retrieval of all orders for a single customer?

A Partition key: OrderID, Sort key: CustomerID

B Partition key: CustomerName, Sort key: OrderDate

C Partition key: CustomerID, Sort key: OrderID

D Partition key: OrderDate, Sort key: CustomerID

💡 Hint

Think about grouping orders by customer for fast lookup.

Using CustomerID as partition key groups all orders per customer. Sort key OrderID uniquely identifies each order within that customer.

❓ service_behavior

advanced

Effect of Missing Sort Key in Composite Key Table

In a DynamoDB table with a composite primary key (partition key + sort key), what happens if you try to put an item without specifying the sort key?

A The operation fails with a validation error

B The item overwrites an existing item with the same partition key

C The item is stored with a null sort key value

D The item is stored but cannot be queried

💡 Hint

Consider the requirement of composite keys in DynamoDB.

DynamoDB requires both partition and sort keys for tables with composite keys. Missing sort key causes a validation error.

❓ security

advanced

Access Control Using Partition Key in IAM Policies

You want to restrict users to access only items with a specific partition key value in a DynamoDB table. Which IAM policy condition key helps enforce this?

A dynamodb:Attributes

B dynamodb:LeadingKeys

C dynamodb:Select

D dynamodb:ReturnConsumedCapacity

💡 Hint

Look for a condition key related to partition key values.

The dynamodb:LeadingKeys condition key restricts access to items with specified partition key values.

✅ Best Practice

expert

Designing Partition and Sort Keys for Hot Partition Avoidance

You have a DynamoDB table storing IoT sensor data with a high write rate. Which key design helps avoid hot partitions?

A Partition key: SensorID#Date, Sort key: Timestamp

B Partition key: Date, Sort key: SensorID

C Partition key: Timestamp, Sort key: SensorID

D Partition key: SensorID, Sort key: Timestamp

💡 Hint

Think about spreading writes across partitions by combining keys.

Combining SensorID and Date in partition key distributes writes across partitions daily, reducing hot partition risk.

Practice

1.

What is the main role of a partition key in AWS DynamoDB?

easy

A. It groups data into partitions for efficient storage and retrieval.

B. It sorts data within a partition in ascending order.

C. It encrypts the data before storing it.

D. It defines the backup schedule for the table.

Solution

1. Step 1: Understand partition key purpose

   The partition key is used to group data into partitions, which helps DynamoDB distribute and store data efficiently.

2. Step 2: Differentiate from sort key

   The sort key orders data inside each partition but does not group data across partitions.

3. Final Answer:

   It groups data into partitions for efficient storage and retrieval. -> Option A

4. Quick Check:

   Partition key = groups data [OK]

Hint: Partition key groups data, sort key orders it inside partitions [OK]

Common Mistakes:

• Confusing partition key with sort key
• Thinking partition key sorts data
• Assuming partition key controls backups

2.

Which of the following is the correct way to define a DynamoDB table with a partition key named UserId and a sort key named OrderDate in AWS CLI?

aws dynamodb create-table --table-name Orders --attribute-definitions AttributeName=UserId,AttributeType=S AttributeName=OrderDate,AttributeType=S --key-schema ...

easy

A. --key-schema AttributeName=UserId,KeyType=HASH AttributeName=OrderDate,KeyType=RANGE

B. --key-schema AttributeName=OrderDate,KeyType=HASH AttributeName=UserId,KeyType=RANGE

C. --key-schema AttributeName=UserId,KeyType=RANGE AttributeName=OrderDate,KeyType=HASH

D. --key-schema AttributeName=OrderDate,KeyType=RANGE AttributeName=UserId,KeyType=HASH

Solution

1. Step 1: Identify partition and sort key roles

   The partition key uses KeyType=HASH and the sort key uses KeyType=RANGE in DynamoDB key schema.

2. Step 2: Match keys to names

   UserId is the partition key (HASH), OrderDate is the sort key (RANGE).

3. Final Answer:

   --key-schema AttributeName=UserId,KeyType=HASH AttributeName=OrderDate,KeyType=RANGE -> Option A

4. Quick Check:

   Partition=HASH, Sort=RANGE [OK]

Hint: Partition key = HASH, sort key = RANGE in key schema [OK]

Common Mistakes:

• Swapping HASH and RANGE key types
• Mixing up partition and sort key names
• Using wrong attribute types

3.

Given a DynamoDB table with CustomerId as partition key and InvoiceDate as sort key, what will the following query return?

Query: KeyConditionExpression = "CustomerId = :cid AND InvoiceDate > :date"

Assuming :cid is '123' and :date is '2023-01-01'.

medium

A. All invoices for customer '123' regardless of date.

B. All invoices for customer '123' with dates after January 1, 2023.

C. All invoices for all customers with dates after January 1, 2023.

D. All invoices with dates before January 1, 2023.

Solution

1. Step 1: Understand KeyConditionExpression

   The query filters items where partition key CustomerId equals '123' and sort key InvoiceDate is greater than '2023-01-01'.

2. Step 2: Interpret the filter effect

   This returns all invoices for customer '123' with InvoiceDate after January 1, 2023.

3. Final Answer:

   All invoices for customer '123' with dates after January 1, 2023. -> Option B

4. Quick Check:

   Partition key = '123' AND sort key > '2023-01-01' [OK]

Hint: Partition key filters customer, sort key filters date range [OK]

Common Mistakes:

• Ignoring partition key filter
• Assuming query returns all customers
• Confusing greater than with less than

4.

What is wrong with this DynamoDB key schema definition?

--attribute-definitions AttributeName=OrderId,AttributeType=S AttributeName=OrderDate,AttributeType=S --key-schema AttributeName=OrderDate,KeyType=HASH AttributeName=OrderId,KeyType=RANGE

medium

A. Attribute names cannot contain uppercase letters.

B. Attribute types must be different for partition and sort keys.

C. KeyType values must both be HASH for composite keys.

D. Partition key and sort key are swapped; OrderId should be HASH, OrderDate RANGE.

Solution

1. Step 1: Check key roles

   Partition key must be HASH and sort key must be RANGE in key schema.

2. Step 2: Identify swapped keys

   OrderId should be the partition key (HASH), but here OrderDate is set as HASH and OrderId as RANGE, which is incorrect.

3. Final Answer:

   Partition key and sort key are swapped; OrderId should be HASH, OrderDate RANGE. -> Option D

4. Quick Check:

   Partition = HASH, Sort = RANGE order matters [OK]

Hint: Partition key always HASH, sort key always RANGE [OK]

Common Mistakes:

• Swapping HASH and RANGE key types
• Assuming attribute types must differ
• Thinking uppercase letters are invalid

5.

You want to design a DynamoDB table to store user activity logs. Each user can have multiple logs per day. Which key design is best to efficiently query all logs for a user on a specific day?

hard

A. Partition key: UserId, Sort key: ActivityDateTime

B. Partition key: ActivityDateTime, Sort key: UserId

C. Partition key: UserId_ActivityDate, Sort key: ActivityTime

D. Partition key: ActivityType, Sort key: UserId

Solution

1. Step 1: Understand query needs

   You want to query logs by user and by specific day efficiently.

2. Step 2: Design keys for efficient queries

   Combining UserId and ActivityDate as partition key groups logs per user per day. Using ActivityTime as sort key orders logs within that day.

3. Final Answer:

   Partition key: UserId_ActivityDate, Sort key: ActivityTime -> Option C

4. Quick Check:

   Composite partition key groups user-day logs [OK]

Hint: Combine user and date in partition key for day queries [OK]

Common Mistakes:

• Using ActivityDateTime as partition key alone
• Swapping partition and sort keys
• Not combining keys to match query pattern