Reserved capacity in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Reserved Capacity in DynamoDB?

Reserved Capacity is a way to pre-pay for a set amount of read and write capacity units in DynamoDB, which can save money compared to on-demand pricing.

beginner

How does Reserved Capacity help with cost management?

By committing to a fixed amount of capacity for a 1 or 3 year term, you get a discount on the hourly rate compared to on-demand usage, helping to reduce costs if your usage is steady.

intermediate

Can Reserved Capacity be shared across multiple DynamoDB tables?

Yes, Reserved Capacity is applied at the AWS account level within a region, so multiple tables can share the reserved capacity you purchase.

intermediate

What happens if your application exceeds the Reserved Capacity limits?

If your usage goes beyond the reserved capacity, DynamoDB will charge you at the on-demand rate for the extra capacity used.

beginner

What are the term options available for Reserved Capacity in DynamoDB?

You can choose Reserved Capacity terms of either 1 year or 3 years, with longer terms offering bigger discounts.

What does Reserved Capacity in DynamoDB primarily help you with?

A Automatically scaling your database

B Saving money by pre-paying for capacity

C Backing up your data

D Encrypting your data

Reserved Capacity lets you pre-pay for read/write units, saving money compared to on-demand pricing.

Can Reserved Capacity be used across multiple tables in the same AWS region?

A Only if tables have the same name

B No, it applies only to one table

C Yes, it is shared across tables in the same region

D Only for tables in different regions

Reserved Capacity is shared at the account level within a region, so multiple tables can use it.

If your usage exceeds your Reserved Capacity, what happens?

A You pay on-demand rates for the extra usage

B You get a refund

C Your database stops working

D AWS automatically increases your reserved capacity

Extra usage beyond reserved capacity is billed at on-demand rates.

What are the available term lengths for Reserved Capacity in DynamoDB?

A 1 year and 3 years

B 6 months and 1 year

C 3 months and 6 months

D No fixed terms

Reserved Capacity can be purchased for 1 or 3 year terms.

Which of the following is NOT a benefit of Reserved Capacity?

A Lower hourly cost for capacity

B Capacity sharing across tables

C Predictable billing

D Automatic scaling of capacity

Reserved Capacity does not automatically scale capacity; it is a fixed pre-purchased amount.

Explain what Reserved Capacity is in DynamoDB and how it can help reduce costs.

Think about paying upfront for a service to get a better price.

Describe how Reserved Capacity is applied across DynamoDB tables and what happens if usage exceeds the reserved amount.

Consider how a shared resource works and what happens when you use more than you reserved.

Practice

1. What is the main benefit of using Reserved Capacity in DynamoDB?

easy

A. It automatically scales the database up and down.

B. It backs up data to another region.

C. It saves money by pre-paying for database capacity.

D. It encrypts data at rest.

Solution

1. Step 1: Understand Reserved Capacity purpose

   Reserved Capacity allows you to pay upfront for a set amount of database throughput, which reduces costs compared to on-demand pricing.

2. Step 2: Compare with other options

   Scaling, backup, and encryption are separate features and not related to Reserved Capacity.

3. Final Answer:

   It saves money by pre-paying for database capacity. -> Option C

4. Quick Check:

   Reserved Capacity = Cost saving by pre-payment [OK]

Hint: Reserved Capacity means paying upfront to save money [OK]

Common Mistakes:

• Confusing Reserved Capacity with auto-scaling
• Thinking it manages backups or encryption
• Assuming it is a query or API feature

2. Which of the following is the correct way to purchase Reserved Capacity for DynamoDB?

easy

A. Through AWS Management Console or AWS CLI

B. Using a SQL query in DynamoDB console

C. By calling a DynamoDB API operation

D. By enabling a setting in the table properties

Solution

1. Step 1: Identify how Reserved Capacity is bought

   Reserved Capacity is purchased via the AWS Management Console or AWS CLI, not through database queries or API calls.

2. Step 2: Eliminate incorrect methods

   SQL queries and table property settings do not handle Reserved Capacity purchases.

3. Final Answer:

   Through AWS Management Console or AWS CLI -> Option A

4. Quick Check:

   Reserved Capacity purchase = Console or CLI [OK]

Hint: Buy Reserved Capacity only via AWS Console or CLI [OK]

Common Mistakes:

• Trying to buy Reserved Capacity with API calls
• Assuming it can be set in table properties
• Confusing it with query commands

3. If a company has a steady workload of 1000 read capacity units and 500 write capacity units, which option best describes the cost benefit of Reserved Capacity?

medium

A. Reserved Capacity saves money by pre-paying for steady usage.

B. Reserved Capacity will cost more than on-demand pricing.

C. Reserved Capacity only applies to burst workloads.

D. Reserved Capacity automatically adjusts capacity units.

Solution

1. Step 1: Understand workload type

   The workload is steady and predictable, which is ideal for Reserved Capacity.

2. Step 2: Match Reserved Capacity benefits

   Reserved Capacity saves money by pre-paying for steady usage, unlike on-demand which is more expensive for constant loads.

3. Final Answer:

   Reserved Capacity saves money by pre-paying for steady usage. -> Option A

4. Quick Check:

   Steady workload + Reserved Capacity = Cost saving [OK]

Hint: Reserved Capacity suits steady workloads to save money [OK]

Common Mistakes:

• Thinking Reserved Capacity is for bursty or variable workloads
• Assuming it auto-scales capacity units
• Believing it costs more than on-demand for steady use

4. A developer tries to buy Reserved Capacity using a DynamoDB API call but gets an error. What is the likely cause?

medium

A. Reserved Capacity requires table to be in on-demand mode.

B. Reserved Capacity cannot be purchased via API calls.

C. The API call syntax is incorrect.

D. Reserved Capacity is only for global tables.

Solution

1. Step 1: Check how Reserved Capacity is purchased

   Reserved Capacity is bought only through AWS Console or CLI, not through DynamoDB API calls.

2. Step 2: Understand error cause

   Trying to buy it via API results in error because the API does not support this operation.

3. Final Answer:

   Reserved Capacity cannot be purchased via API calls. -> Option B

4. Quick Check:

   Reserved Capacity purchase method = Console/CLI only [OK]

Hint: Reserved Capacity purchase via API causes error [OK]

Common Mistakes:

• Assuming API calls can buy Reserved Capacity
• Blaming syntax errors without checking purchase method
• Confusing Reserved Capacity with table modes

5. A company has unpredictable spikes in traffic but wants to save costs using Reserved Capacity. What is the best approach?

hard

A. Reserved Capacity automatically adjusts to spikes, so buy any amount.

B. Buy Reserved Capacity for the peak traffic to cover all spikes.

C. Use only on-demand capacity to handle spikes efficiently.

D. Buy Reserved Capacity for the average baseline and use on-demand for spikes.

Solution

1. Step 1: Analyze workload pattern

   The workload has unpredictable spikes, so buying Reserved Capacity for peak would be costly and wasteful.

2. Step 2: Combine Reserved and on-demand

   Buying Reserved Capacity for the steady baseline and using on-demand for spikes balances cost and flexibility.

3. Final Answer:

   Buy Reserved Capacity for the average baseline and use on-demand for spikes. -> Option D

4. Quick Check:

   Baseline Reserved + on-demand spikes = Cost efficient [OK]

Hint: Reserve baseline, use on-demand for spikes to save money [OK]

Common Mistakes:

• Buying Reserved Capacity for peak traffic wastes money
• Relying only on on-demand increases cost
• Thinking Reserved Capacity auto-scales with spikes