DynamoDB capacity modes (on-demand, provisioned) in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the On-Demand capacity mode in DynamoDB?

On-Demand capacity mode lets DynamoDB handle all the read and write traffic automatically. You pay only for the requests you use, without setting capacity limits.

beginner

What does Provisioned capacity mode require you to do in DynamoDB?

Provisioned capacity mode requires you to specify the number of reads and writes per second your table needs. You pay for this capacity whether you use it or not.

intermediate

When should you choose On-Demand capacity mode?

Choose On-Demand if your app has unpredictable or variable traffic. It scales automatically and is simple to use without capacity planning.

intermediate

What is a benefit of Provisioned capacity mode?

Provisioned mode can be more cost-effective for steady, predictable workloads because you pay a fixed rate for capacity.

intermediate

What happens if your app exceeds Provisioned capacity limits in DynamoDB?

If you exceed provisioned capacity, requests may be throttled, causing delays or errors until capacity is increased or traffic decreases.

Which DynamoDB capacity mode automatically adjusts to your app's traffic without manual setup?

A On-Demand

B Provisioned

C Reserved

D Manual

On-Demand mode automatically handles traffic and scales without manual capacity settings.

In Provisioned capacity mode, what do you need to specify?

A Number of reads and writes per second

B Total data size

C Number of tables

D Backup frequency

Provisioned mode requires setting read and write capacity units per second.

What is a risk of using Provisioned capacity mode with unpredictable traffic?

A Automatic scaling

B Lower cost

C Throttling when traffic spikes

D Unlimited requests

If traffic exceeds provisioned limits, requests can be throttled causing delays.

Which capacity mode charges you only for the requests you make?

A Fixed

B Provisioned

C Reserved

D On-Demand

On-Demand charges based on actual request usage, no fixed capacity.

For a steady workload with predictable traffic, which mode is usually more cost-effective?

A Manual

B Provisioned

C Burst

D On-Demand

Provisioned mode is cheaper for steady, predictable workloads due to fixed capacity pricing.

Explain the main differences between DynamoDB's On-Demand and Provisioned capacity modes.

Think about how each mode handles traffic and billing.

Describe what happens if your application exceeds the Provisioned capacity limits in DynamoDB.

Consider the impact on app performance and user experience.

Practice

1. What is the main advantage of using DynamoDB's on-demand capacity mode?

easy

A. It offers a lower cost for steady, predictable workloads.

B. It automatically scales to handle any workload without manual capacity planning.

C. It requires you to set fixed read and write capacity units.

D. It limits the number of requests per second to a fixed amount.

Solution

1. Step 1: Understand on-demand mode behavior

   On-demand mode automatically adjusts capacity to meet traffic demands without manual input.

2. Step 2: Compare with provisioned mode

   Provisioned mode requires fixed capacity settings, unlike on-demand.

3. Final Answer:

   It automatically scales to handle any workload without manual capacity planning. -> Option B

4. Quick Check:

   On-demand = auto scaling without setup [OK]

Hint: On-demand means auto scale, no manual setup needed [OK]

Common Mistakes:

• Confusing on-demand with provisioned fixed capacity
• Thinking on-demand limits requests
• Assuming on-demand is cheaper for steady workloads

2. Which of the following is the correct way to specify provisioned capacity in a DynamoDB table creation JSON?

easy

A. { "Throughput": { "Reads": 5, "Writes": 10 } }

B. { "CapacityMode": "ON_DEMAND" }

C. { "ProvisionedThroughput": { "ReadCapacityUnits": 5, "WriteCapacityUnits": 10 } }

D. { "ReadUnits": 5, "WriteUnits": 10 }

Solution

1. Step 1: Recall provisioned capacity syntax

   Provisioned mode requires specifying ReadCapacityUnits and WriteCapacityUnits inside ProvisionedThroughput.

2. Step 2: Check options for correct JSON structure

   { "ProvisionedThroughput": { "ReadCapacityUnits": 5, "WriteCapacityUnits": 10 } } matches the correct AWS DynamoDB API format for provisioned throughput.

3. Final Answer:

   { "ProvisionedThroughput": { "ReadCapacityUnits": 5, "WriteCapacityUnits": 10 } } -> Option C

4. Quick Check:

   ProvisionedThroughput with Read/Write units = correct syntax [OK]

Hint: Provisioned capacity uses ProvisionedThroughput with Read/Write units [OK]

Common Mistakes:

• Using CapacityMode for provisioned capacity
• Missing ProvisionedThroughput wrapper
• Incorrect property names like ReadUnits

3. Given a DynamoDB table in provisioned mode with 5 read capacity units and 5 write capacity units, what happens if your application suddenly sends 20 write requests per second?

medium

A. Some write requests are throttled because they exceed the provisioned write capacity.

B. All 20 write requests succeed immediately without throttling.

C. DynamoDB automatically increases write capacity to 20 units instantly.

D. The table switches automatically to on-demand mode to handle the load.

Solution

1. Step 1: Understand provisioned capacity limits

   Provisioned mode limits throughput to the set capacity units (5 writes per second here).

2. Step 2: Analyze effect of exceeding capacity

   Sending 20 writes exceeds 5 units, causing throttling of excess requests.

3. Final Answer:

   Some write requests are throttled because they exceed the provisioned write capacity. -> Option A

4. Quick Check:

   Provisioned mode throttles excess requests [OK]

Hint: Provisioned mode throttles requests above set capacity [OK]

Common Mistakes:

• Assuming automatic capacity increase in provisioned mode
• Thinking on-demand mode applies automatically
• Believing all requests always succeed

4. You configured a DynamoDB table with provisioned capacity: 10 read units and 10 write units. Your application experiences throttling errors during peak hours. What is the best immediate fix to reduce throttling without downtime?

medium

A. Switch the table to on-demand capacity mode.

B. Reduce the size of items stored in the table.

C. Delete and recreate the table with higher capacity.

D. Increase the provisioned read and write capacity units.

Solution

1. Step 1: Identify cause of throttling

   Throttling occurs because provisioned capacity is too low for peak traffic.

2. Step 2: Choose immediate fix without downtime

   Increasing provisioned capacity units can be done live without deleting the table.

3. Final Answer:

   Increase the provisioned read and write capacity units. -> Option D

4. Quick Check:

   Increase capacity units to reduce throttling [OK]

Hint: Increase provisioned units live to fix throttling fast [OK]

Common Mistakes:

• Deleting and recreating table causes downtime
• Assuming switching to on-demand is instant and free
• Reducing item size does not fix capacity limits

5. A startup expects unpredictable traffic spikes and wants to minimize cost during low usage while avoiding throttling during spikes. Which DynamoDB capacity mode should they choose and why?

hard

A. On-demand mode because it charges per request and scales instantly without manual setup.

B. Provisioned mode with auto scaling enabled to adjust capacity automatically.

C. Provisioned mode with fixed capacity to control costs strictly.

D. On-demand mode but with a fixed maximum request limit to save costs.

Solution

1. Step 1: Understand startup's needs

   They want to avoid throttling during spikes and save cost during low usage.

2. Step 2: Compare capacity modes for unpredictable traffic

   On-demand mode charges per request and auto scales instantly, ideal for unpredictable spikes.

3. Step 3: Evaluate other options

   Provisioned with auto scaling helps but requires setup and may lag; fixed capacity risks throttling or cost waste.

4. Final Answer:

   On-demand mode because it charges per request and scales instantly without manual setup. -> Option A

5. Quick Check:

   Unpredictable traffic = on-demand mode best [OK]

Hint: Unpredictable spikes? Choose on-demand for auto scaling [OK]

Common Mistakes:

• Choosing fixed provisioned capacity for unpredictable traffic
• Assuming auto scaling is instant and always perfect
• Thinking on-demand has fixed request limits