Identifying access patterns first in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the primary key attribute name in a DynamoDB table creation.

DynamoDB

KeySchema: [{ AttributeName: [1], KeyType: 'HASH' }]

Drag options to blanks, or click blank then click option'

AUserId

BTimestamp

CEmail

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a non-unique attribute like 'Status' as primary key.

The primary key attribute name is usually a unique identifier like 'UserId'.

2fill in blank

medium

Complete the code to define a Global Secondary Index (GSI) partition key.

DynamoDB

GlobalSecondaryIndexes: [{ IndexName: 'StatusIndex', KeySchema: [{ AttributeName: [1], KeyType: 'HASH' }] }]

Drag options to blanks, or click blank then click option'

AUserId

BEmail

CTimestamp

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using the primary key attribute 'UserId' as GSI key.

The GSI partition key is often an attribute like 'Status' to query items by their status.

3fill in blank

hard

Fix the error in the query to get an item by primary key.

DynamoDB

const params = { TableName: 'Users', Key: { [1]: '12345' } };

Drag options to blanks, or click blank then click option'

AStatus

BEmail

CUserId

DTimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-primary key attribute in the Key object.

The Key must use the primary key attribute name, which is 'UserId' here.

4fill in blank

hard

Fill both blanks to create a query using a GSI to find items by status and sort by timestamp.

DynamoDB

const params = { TableName: 'Orders', IndexName: 'StatusIndex', KeyConditionExpression: '[1] = :statusVal AND [2] > :timeVal', ExpressionAttributeValues: { ':statusVal': 'shipped', ':timeVal': 1609459200 } };

Drag options to blanks, or click blank then click option'

AStatus

BUserId

CTimestamp

DOrderId

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping partition and sort key names.

The query uses 'Status' as the partition key and 'Timestamp' as the sort key in the GSI.

5fill in blank

hard

Fill all three blanks to create a DynamoDB update expression that sets a new status and increments a counter.

DynamoDB

const params = { TableName: 'Tasks', Key: { TaskId: 'task123' }, UpdateExpression: 'SET [1] = :newStatus, [2] = [3] + :inc', ExpressionAttributeValues: { ':newStatus': 'completed', ':inc': 1 } };

Drag options to blanks, or click blank then click option'

AStatus

BCounter

CCount

DProgress

Attempts:

3 left

💡 Hint

Common Mistakes

Using different attribute names for increment operation.

The update expression sets the 'Status' attribute and increments the 'Count' attribute by 1.

Practice

1. Why is it important to identify access patterns before designing a DynamoDB table?

easy

A. Because it tells how many users will use the app.

B. Because it helps to choose the right programming language for the app.

C. Because access patterns determine the keys and indexes needed for efficient queries.

D. Because it decides the color scheme of the app interface.

Solution

1. Step 1: Understand the role of access patterns

   Access patterns describe how the app will retrieve data, which guides table design.

2. Step 2: Connect access patterns to keys and indexes

   Keys and indexes in DynamoDB are chosen based on these patterns to make queries fast and efficient.

3. Final Answer:

   Because access patterns determine the keys and indexes needed for efficient queries. -> Option C

4. Quick Check:

   Access patterns = keys/indexes choice [OK]

Hint: Access patterns guide key/index design for fast queries [OK]

Common Mistakes:

• Thinking access patterns affect UI design
• Confusing access patterns with user count
• Believing access patterns decide programming language

2. Which of the following is the correct way to describe an access pattern in DynamoDB?

easy

A. A list of all table columns.

B. A query that the app will run to get data.

C. The number of items in the table.

D. The size of the database backup.

Solution

1. Step 1: Define what an access pattern is

   An access pattern is a way the app queries or retrieves data from the database.

2. Step 2: Match the options to this definition

   Only "A query that the app will run to get data." describes a query the app will run, which fits the access pattern meaning.

3. Final Answer:

   A query that the app will run to get data. -> Option B

4. Quick Check:

   Access pattern = app query [OK]

Hint: Access pattern means how app queries data [OK]

Common Mistakes:

• Confusing access pattern with table schema
• Thinking access pattern is about data size
• Mixing access pattern with backup info

3. Given an app needs to get user orders by user ID and order date, which access pattern should be planned first?

medium

A. Query orders by user ID and sort by order date.

B. Scan all orders and filter by user ID.

C. Get orders by order date only.

D. Query orders by product ID.

Solution

1. Step 1: Identify the required data retrieval

   The app needs orders filtered by user ID and sorted by order date.

2. Step 2: Choose the access pattern matching this need

   Querying by user ID and sorting by order date matches the requirement and is efficient.

3. Final Answer:

   Query orders by user ID and sort by order date. -> Option A

4. Quick Check:

   Access pattern = query by user ID + order date [OK]

Hint: Match access pattern to app's data retrieval need [OK]

Common Mistakes:

• Using scan instead of query causes slow performance
• Ignoring sorting by order date
• Querying by unrelated keys like product ID

4. You designed a DynamoDB table without identifying access patterns first. Your app queries are slow. What is the likely cause?

medium

A. The table keys and indexes do not support the app's query needs.

B. The app has too many users.

C. The table has too many columns.

D. The app is using the wrong programming language.

Solution

1. Step 1: Understand the impact of missing access pattern planning

   Without access patterns, keys and indexes may not match query needs, causing slow queries.

2. Step 2: Eliminate unrelated causes

   User count, column number, or programming language do not directly cause slow DynamoDB queries.

3. Final Answer:

   The table keys and indexes do not support the app's query needs. -> Option A

4. Quick Check:

   Missing access patterns = wrong keys/indexes = slow queries [OK]

Hint: Slow queries often mean keys/indexes mismatch access patterns [OK]

Common Mistakes:

• Blaming app user count for query speed
• Thinking table columns affect query speed directly
• Assuming programming language affects DynamoDB speed

5. An app needs to retrieve customer profiles by email and also list all customers in a city. How should you identify access patterns to design the DynamoDB table?

hard

A. Store all customers in one table without keys and scan for queries.

B. Create separate tables for email and city queries.

C. Use email as the only key and ignore city queries.

D. Plan one access pattern to query by email and another to query by city using a secondary index.

Solution

1. Step 1: Identify the two access patterns

   The app needs to get customers by email and also list customers by city.

2. Step 2: Design keys and indexes accordingly

   Use email as the primary key and create a secondary index on city to support both queries efficiently.

3. Final Answer:

   Plan one access pattern to query by email and another to query by city using a secondary index. -> Option D

4. Quick Check:

   Multiple access patterns = primary key + secondary index [OK]

Hint: Use secondary indexes for multiple access patterns [OK]

Common Mistakes:

• Ignoring secondary indexes for city queries
• Using scans instead of queries
• Creating separate tables unnecessarily