Reserved capacity in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Reserved Capacity Billing

Which statement best describes how reserved capacity affects billing in DynamoDB?

A Reserved capacity only applies to on-demand tables and charges per request.

B Reserved capacity automatically increases your table's throughput without extra cost.

C Reserved capacity allows unlimited storage without additional charges.

D Reserved capacity provides a discount by pre-purchasing read and write capacity units for a fixed term.

💡 Hint

Think about how pre-purchasing capacity units can save money.

Reserved capacity lets you commit to a set amount of read and write capacity units for a 1- or 3-year term, which reduces costs compared to on-demand pricing.

❓ query_result

intermediate

Reserved Capacity Impact on Cost Calculation

Given a DynamoDB table with 100 reserved write capacity units and actual usage of 150 write capacity units in a billing hour, how many write capacity units are billed at the on-demand rate?

A 50 write capacity units

B 100 write capacity units

C 150 write capacity units

D 0 write capacity units

💡 Hint

Reserved capacity covers part of the usage; the rest is billed on-demand.

The reserved capacity covers 100 units. The extra 50 units (150 - 100) are billed at the on-demand rate.

📝 Syntax

advanced

Reserved Capacity Purchase CLI Command

Which AWS CLI command correctly purchases reserved capacity for DynamoDB with 200 write capacity units for 1 year?

A aws dynamodb purchase-reserved-capacity --reserved-capacity-configuration WriteCapacityUnits=200,Duration=1

B aws dynamodb purchase-reserved-capacity-offering --reserved-capacity-offering-id 200 --count 1

C aws dynamodb purchase-reserved-capacity-offering --reserved-capacity-offering-id <offering-id> --count 1

D aws dynamodb buy-reserved-capacity --write-units 200 --term 1

💡 Hint

You need to specify the offering ID, not just the units.

The correct command requires the reserved capacity offering ID and the count of units to purchase. You must first describe offerings to get the ID.

❓ optimization

advanced

Optimizing Reserved Capacity Usage

You have multiple DynamoDB tables with varying workloads. How can you optimize reserved capacity purchases to reduce costs?

A Use on-demand capacity mode only to avoid managing reserved capacity.

B Purchase reserved capacity at the account level to share across tables and reduce unused capacity.

C Purchase reserved capacity for each table separately based on its peak usage.

D Purchase reserved capacity only for the largest table and let others use on-demand.

💡 Hint

Think about sharing capacity across tables to maximize utilization.

Reserved capacity is shared across all tables in the account, so buying at the account level allows unused capacity from one table to cover others, reducing waste.

🔧 Debug

expert

Troubleshooting Reserved Capacity Not Applying

You purchased reserved capacity for 300 read units, but your billing shows you are still charged on-demand for all 300 read units. What is the most likely cause?

A The reserved capacity was purchased in a different AWS region than the table's region.

B Reserved capacity only applies to write units, not read units.

C You must enable reserved capacity on each table manually after purchase.

D Reserved capacity applies only to on-demand tables, not provisioned tables.

💡 Hint

Check if the reserved capacity and table are in the same region.

Reserved capacity is region-specific. If purchased in a different region, it won't apply to tables in another region, causing on-demand charges.