DEA-C01 Global Secondary Index (GSI) Practice Question
A company runs a streaming application on Amazon EC2 instances that writes data to an Amazon DynamoDB table (us-east-1). The data is later consumed by a reporting job that runs every hour. Recently, the reporting job has been failing with ProvisionedThroughputExceededException errors during peak hours. The DynamoDB table uses provisioned capacity with 1000 read capacity units (RCU) and 500 write capacity units (WCU). The reporting job performs scans and reads using eventually consistent reads. The application's write traffic is steady, but the reporting job's reads spike at the top of the hour. The data engineer needs to resolve the throughput exceptions without affecting the application's writes. Which solution should the data engineer implement?
⚠ Common exam trap
The main trap is thinking that simply increasing the table's RCU or switching to on-demand is the best solution, without considering the impact on write performance or cost. A GSI with dedicated capacity isolates read workloads.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a global secondary index (GSI) with enough RCU for the reporting job and have the job query the index instead of scanning the table.
The reporting job is failing due to ProvisionedThroughputExceededException because it performs full table scans, consuming read capacity from the table's provisioned RCU. Since the write traffic is steady and must not be affected, increasing the table's RCU (Option B) is not ideal because it would also allow more reads, potentially impacting writes if capacity is shared. Switching to on-demand (Option D) would eliminate throttling but could significantly increase costs and does not provide dedicated read capacity for the reporting job. A read replica (Option C) is not a native DynamoDB feature. Creating a global secondary index (GSI) with its own provisioned read capacity dedicated for the reporting job (Option A) offloads the read traffic from the main table, preventing interference with writes. The job can query the GSI with eventually consistent reads, effectively using the allocated RCU on the GSI without affecting the table's capacity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create a global secondary index (GSI) with enough RCU for the reporting job and have the job query the index instead of scanning the table.
Why this is correct
Correct. Adding a GSI with its own RCU allows the reporting job to read from the index without consuming the table's RCU, avoiding throttling and not affecting writes.
- ✗
Increase the table's RCU to 2000.
Why it's wrong here
Incorrect. Increasing table RCU would allow more reads but does not isolate the reporting workload from writes and may still lead to contention.
- ✗
Create a read replica of the DynamoDB table in a different region.
Why it's wrong here
Incorrect. DynamoDB does not support read replicas across regions; this is not a valid solution.
- ✗
Switch the table to on-demand capacity mode.
Why it's wrong here
Incorrect. On-demand mode eliminates throttling but can be more expensive and does not guarantee performance isolation between reads and writes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.