Stream vs polling comparison in DynamoDB - Hands-On Comparison

Stream vs Polling Comparison in DynamoDB

📖 Scenario: You are building a simple inventory tracking system using DynamoDB. You want to understand how to detect changes in your inventory data efficiently.Two common methods are DynamoDB Streams and polling the table for changes. This project will help you set up both methods step-by-step to compare how they work.

🎯 Goal: Build a DynamoDB table with sample inventory data, configure a stream on the table, and write a polling query to fetch recent changes. This will help you see the difference between using streams and polling for data updates.

📋 What You'll Learn

Create a DynamoDB table named Inventory with a primary key ItemID.

Insert sample items with exact ItemID and Quantity values.

Enable DynamoDB Streams on the Inventory table with NEW_IMAGE view type.

Write a polling query to scan the Inventory table for items with Quantity less than 10.

💡 Why This Matters

🌍 Real World

Many applications need to react to data changes in real time. DynamoDB Streams provide an efficient way to capture these changes without repeatedly scanning the table.

💼 Career

Understanding streams and polling is important for backend developers and cloud engineers working with AWS DynamoDB to build scalable and responsive applications.

1

Create DynamoDB Table and Insert Sample Data

Create a DynamoDB table called Inventory with ItemID as the primary key (string). Insert these exact items into the table: {"ItemID": "A101", "Quantity": 15}, {"ItemID": "B202", "Quantity": 8}, and {"ItemID": "C303", "Quantity": 20}.

DynamoDB

# Create the Inventory table and insert the sample items
# Your code here

Hint

Use AWS CLI commands create-table and put-item with exact attribute names and values.

2

Enable DynamoDB Streams on the Inventory Table

Enable DynamoDB Streams on the Inventory table with the stream view type set to NEW_IMAGE.

DynamoDB

aws dynamodb create-table --table-name Inventory --attribute-definitions AttributeName=ItemID,AttributeType=S --key-schema AttributeName=ItemID,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "A101"}, "Quantity": {"N": "15"}}'
aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "B202"}, "Quantity": {"N": "8"}}'
aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "C303"}, "Quantity": {"N": "20"}}'

# Enable DynamoDB Streams with NEW_IMAGE view type
# Your code here

Hint

Use the update-table command with --stream-specification to enable streams.

3

Write a Polling Query to Find Low Stock Items

Write a DynamoDB scan command to find items in the Inventory table where Quantity is less than 10.

DynamoDB

aws dynamodb create-table --table-name Inventory --attribute-definitions AttributeName=ItemID,AttributeType=S --key-schema AttributeName=ItemID,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "A101"}, "Quantity": {"N": "15"}}'
aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "B202"}, "Quantity": {"N": "8"}}'
aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "C303"}, "Quantity": {"N": "20"}}'

aws dynamodb update-table --table-name Inventory --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE

# Write a scan command to find items with Quantity less than 10
# Your code here

Hint

Use the scan command with a filter expression to find items with Quantity less than 10.

4

Complete Setup by Describing the Stream ARN

Add a command to describe the Inventory table and show the Stream ARN to confirm the stream is enabled.

DynamoDB

aws dynamodb create-table --table-name Inventory --attribute-definitions AttributeName=ItemID,AttributeType=S --key-schema AttributeName=ItemID,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "A101"}, "Quantity": {"N": "15"}}'
aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "B202"}, "Quantity": {"N": "8"}}'
aws dynamodb put-item --table-name Inventory --item '{"ItemID": {"S": "C303"}, "Quantity": {"N": "20"}}'

aws dynamodb update-table --table-name Inventory --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE

aws dynamodb scan --table-name Inventory --filter-expression "Quantity < :val" --expression-attribute-values '{":val":{"N":"10"}}'

# Describe the Inventory table to show the Stream ARN
# Your code here

Hint

Use the describe-table command with a query to show the Stream ARN.

Practice

1. Which of the following best describes DynamoDB Streams compared to polling?

easy

A. Polling and streams both check for changes only once a day.

B. Polling pushes data changes immediately, streams check periodically.

C. Streams push data changes immediately, polling checks periodically.

D. Both streams and polling push data changes immediately.

Solution

1. Step 1: Understand DynamoDB Streams behavior

   DynamoDB Streams send data change events as they happen, pushing updates immediately.

2. Step 2: Understand polling behavior

   Polling requires the client to ask for updates at fixed intervals, not instantly.

3. Final Answer:

   Streams push data changes immediately, polling checks periodically. -> Option C

4. Quick Check:

   Streams = push, Polling = periodic check [OK]

Hint: Streams push instantly; polling waits for your request [OK]

Common Mistakes:

• Confusing which method pushes data
• Thinking polling is real-time
• Assuming streams require manual checks

2. Which syntax correctly represents enabling DynamoDB Streams on a table using AWS CLI?

easy

A. aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE

B. aws dynamodb enable-stream --table MyTable --type NEW_IMAGE

C. aws dynamodb create-stream --table-name MyTable --view NEW_IMAGE

D. aws dynamodb set-stream --table MyTable --enabled true

Solution

1. Step 1: Identify correct AWS CLI command for streams

   The correct command to enable streams is 'update-table' with '--stream-specification' option.

2. Step 2: Verify syntax correctness

   aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE uses correct flags and parameters: StreamEnabled=true and StreamViewType=NEW_IMAGE.

3. Final Answer:

   aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE -> Option A

4. Quick Check:

   Enable streams with update-table and stream-specification [OK]

Hint: Use update-table with --stream-specification to enable streams [OK]

Common Mistakes:

• Using non-existent commands like create-stream
• Incorrect flag names
• Missing StreamEnabled parameter

3. Given a DynamoDB table with streams enabled, what will happen if you poll the table every 10 minutes instead of using streams?

medium

A. Polling disables streams temporarily.

B. You get real-time updates as soon as data changes.

C. Polling automatically triggers streams to push data.

D. You receive updates only every 10 minutes, possibly missing immediate changes.

Solution

1. Step 1: Understand polling frequency impact

   Polling every 10 minutes means updates are checked only at those intervals, not instantly.

2. Step 2: Compare with streams behavior

   Streams push changes immediately, so polling delays updates and may miss real-time events.

3. Final Answer:

   You receive updates only every 10 minutes, possibly missing immediate changes. -> Option D

4. Quick Check:

   Polling = delayed updates, not real-time [OK]

Hint: Polling delays updates; streams push instantly [OK]

Common Mistakes:

• Assuming polling is real-time
• Thinking polling triggers streams
• Believing polling disables streams

4. You wrote code to poll a DynamoDB table every 5 seconds but notice high latency and missed updates. What is the likely issue?

medium

A. Streams must be disabled to use polling.

B. Polling too frequently causes throttling and delays.

C. Polling automatically disables table writes.

D. Polling every 5 seconds guarantees no missed updates.

Solution

1. Step 1: Analyze polling frequency effects

   Polling very frequently can cause throttling or API limits, increasing latency.

2. Step 2: Understand polling limitations

   Polling does not guarantee no missed updates and can overload the system if too frequent.

3. Final Answer:

   Polling too frequently causes throttling and delays. -> Option B

4. Quick Check:

   Too frequent polling = throttling and latency [OK]

Hint: Avoid polling too often to prevent throttling [OK]

Common Mistakes:

• Thinking streams must be off to poll
• Believing polling disables writes
• Assuming frequent polling prevents missed updates

5. You need to build a dashboard that updates instantly when DynamoDB data changes. Which approach is best and why?

hard

A. Use DynamoDB Streams to push changes and update dashboard in real-time.

B. Poll the table every hour to reduce costs and update dashboard.

C. Disable streams and poll every 5 minutes for near real-time updates.

D. Use polling once a day and cache results for dashboard.

Solution

1. Step 1: Identify real-time update requirement

   The dashboard needs instant updates when data changes, requiring immediate notification.

2. Step 2: Compare streams and polling for real-time needs

   Streams push changes immediately, ideal for real-time dashboards; polling delays updates and is less efficient.

3. Final Answer:

   Use DynamoDB Streams to push changes and update dashboard in real-time. -> Option A

4. Quick Check:

   Real-time dashboard = use streams [OK]

Hint: For instant updates, prefer streams over polling [OK]

Common Mistakes:

• Choosing polling despite real-time need
• Ignoring cost vs latency trade-offs
• Assuming polling can be truly real-time