Reserved capacity in DynamoDB

Introduction

Reserved capacity helps you save money by paying upfront for a set amount of database capacity instead of paying for it as you go.

You know your app will need a steady amount of database power for a long time.

You want to reduce costs for your database usage by committing ahead.

You want to avoid surprises from sudden spikes in database charges.

You have a predictable workload and want to plan your budget better.

Syntax

DynamoDB

Reserved capacity is purchased through AWS Management Console or AWS CLI, not by a direct query.
You specify:
- Capacity units (read/write)
- Duration (usually 1 or 3 years)
- Payment option (all upfront, partial, or monthly)

Reserved capacity is not a query but a billing option you set up before using the database.

It applies to your whole account.

Examples

This AWS CLI command buys 5 units of reserved capacity for DynamoDB.

DynamoDB

aws dynamodb purchase-reserved-capacity-offering --reserved-capacity-offering-id <offering-id> --reserved-capacity-quantity 5

This is how you buy reserved capacity using the AWS web interface.

DynamoDB

In AWS Console, go to DynamoDB > Reserved Capacity > Purchase
Select capacity units and payment plan
Confirm purchase

Sample Program

This command purchases 10 reserved capacity units using the specified offering ID.

DynamoDB

-- Reserved capacity is not created by SQL or query language.
-- Instead, you buy it via AWS CLI or Console.
-- Example CLI command:
aws dynamodb purchase-reserved-capacity-offering --reserved-capacity-offering-id abc123 --reserved-capacity-quantity 10

Important Notes

Reserved capacity reduces your hourly cost but requires upfront commitment.

You cannot query reserved capacity like data; it is a billing setting.

Make sure to estimate your needs carefully before purchasing.

Summary

Reserved capacity saves money by pre-paying for database power.

It is bought through AWS Console or CLI, not by database queries.

Best for steady, predictable workloads to control costs.

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