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Monitoring and Troubleshooting →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to change the DB instance class from db.t3.medium to a dedicated CPU instance like db.r5.large because the root cause is CPU credit exhaustion on the T3 instance. Even though CPUUtilization sits below 50%, a T3 medium’s baseline is only about 10% of a vCPU; once the CPUCreditBalance hits zero, the instance is throttled to that baseline, which starves simple SELECT statements of processing power and spikes latency from 5 ms to over 500 ms. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding that burstable T3 instances are unsuitable for steady-state, high-traffic workloads, and that Performance Insights metrics like db.sql.queries.avg_latency combined with a near-zero CPUCreditBalance are the definitive diagnostic signal. A common trap is assuming low CPU utilization means no CPU bottleneck, but T3 credits decouple utilization from available performance. Memory tip: “Zero credits, zero burst—switch to R5 or you’ll thirst.”

DBS-C01 Monitoring and Troubleshooting Practice Question

This DBS-C01 practice question tests your understanding of monitoring and troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

You are managing an Amazon RDS for PostgreSQL Multi-AZ DB instance that handles a high-traffic e-commerce application. Recently, the database has been experiencing intermittent slowdowns during peak hours. You have enabled Enhanced Monitoring and Performance Insights. After reviewing the Performance Insights dashboard, you notice that the 'db.sql.queries.avg_latency' metric spikes during the slowdowns, and the top SQL queries are all simple SELECT statements on a frequently accessed 'orders' table. The table has over 10 million rows and is indexed on 'order_id', 'customer_id', and 'order_date'. The average query latency for these SELECT statements jumps from 5 ms to over 500 ms during the spikes. You also observe that the 'ReadIOPS' metric on the DB instance is consistently below the provisioned IOPS limit of the gp2 storage. The DB instance type is db.r5.large with 16 GB memory. The 'DatabaseConnections' metric shows that the number of connections is well within the max_connections limit (set to 200). However, the 'CPUCreditBalance' for the underlying EC2 instance, which is a T3 medium, drops to near zero during the spikes. The 'CPUUtilization' metric is below 50%. Which of the following is the MOST likely cause and the appropriate action to resolve the issue?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1hardmultiple choice

Full question →

A
The issue is due to CPU credit exhaustion on the T3 instance. Change the DB instance class from db.t3.medium to a dedicated CPU instance type such as db.r5.large.
The T3 instance uses CPU credits; when credits are exhausted, performance is throttled. Changing to a dedicated instance eliminates credit-based performance.
B
The issue is due to a memory bottleneck causing queries to spill to disk. Increase the instance memory by moving to a db.r5.xlarge instance.
Why wrong: Memory pressure would show high SwapUsage or low FreeableMemory, not CPU credit exhaustion. The instance is db.r5.large, not T3.
C
The issue is caused by a connection pool exhaustion. Increase the max_connections parameter and use connection pooling.
Why wrong: Connection count is well below max_connections, so this is not the issue. CPU credit exhaustion is the clear symptom.
D
The issue is caused by a missing index on the 'orders' table. Add a composite index on the columns used in the WHERE clauses.
Why wrong: Missing indexes would cause high ReadIOPS and sequential scans, but ReadIOPS is low and the table has indexes. The symptom points to CPU throttling.

Full breakdown with real-world context →

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

✓

The issue is due to CPU credit exhaustion on the T3 instance. Change the DB instance class from db.t3.medium to a dedicated CPU instance type such as db.r5.large.

The correct answer is A. The 'CPUCreditBalance' dropping to near zero on a T3 instance indicates CPU credit exhaustion, which throttles the baseline CPU performance and causes query latency spikes. Even though 'CPUUtilization' is below 50%, T3 instances rely on CPU credits for burstable performance; when credits are exhausted, the instance is limited to the baseline (e.g., 10% for t3.medium), causing severe latency increases for simple SELECT statements. Moving to a dedicated CPU instance like db.r5.large eliminates credit-based throttling and provides consistent performance.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
The issue is due to CPU credit exhaustion on the T3 instance. Change the DB instance class from db.t3.medium to a dedicated CPU instance type such as db.r5.large.
Why this is correct
The T3 instance uses CPU credits; when credits are exhausted, performance is throttled. Changing to a dedicated instance eliminates credit-based performance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The issue is due to a memory bottleneck causing queries to spill to disk. Increase the instance memory by moving to a db.r5.xlarge instance.
Why it's wrong here
Memory pressure would show high SwapUsage or low FreeableMemory, not CPU credit exhaustion. The instance is db.r5.large, not T3.
✗
The issue is caused by a connection pool exhaustion. Increase the max_connections parameter and use connection pooling.
Why it's wrong here
Connection count is well below max_connections, so this is not the issue. CPU credit exhaustion is the clear symptom.
✗
The issue is caused by a missing index on the 'orders' table. Add a composite index on the columns used in the WHERE clauses.
Why it's wrong here
Missing indexes would cause high ReadIOPS and sequential scans, but ReadIOPS is low and the table has indexes. The symptom points to CPU throttling.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates see low CPU utilization and assume no CPU issue, but T3 instances can be throttled even at moderate utilization when credits are exhausted, and the 'CPUCreditBalance' metric is the key indicator.

Trap categories for this question

Command / output trap
Memory pressure would show high SwapUsage or low FreeableMemory, not CPU credit exhaustion. The instance is db.r5.large, not T3.

Detailed technical explanation

How to think about this question

T3 instances use a CPU credit mechanism where each credit provides one minute of 100% CPU utilization; when credits are exhausted, the instance is throttled to the baseline (e.g., 10% for t3.medium). Even at 50% CPU utilization, the instance may be starved for credits if the workload is bursty, causing intermittent latency spikes. Performance Insights shows 'db.sql.queries.avg_latency' spikes because the CPU cannot process queries quickly enough, despite low ReadIOPS and sufficient memory.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this DBS-C01 question test?

Monitoring and Troubleshooting — This question tests Monitoring and Troubleshooting — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The issue is due to CPU credit exhaustion on the T3 instance. Change the DB instance class from db.t3.medium to a dedicated CPU instance type such as db.r5.large. — The correct answer is A. The 'CPUCreditBalance' dropping to near zero on a T3 instance indicates CPU credit exhaustion, which throttles the baseline CPU performance and causes query latency spikes. Even though 'CPUUtilization' is below 50%, T3 instances rely on CPU credits for burstable performance; when credits are exhausted, the instance is limited to the baseline (e.g., 10% for t3.medium), causing severe latency increases for simple SELECT statements. Moving to a dedicated CPU instance like db.r5.large eliminates credit-based throttling and provides consistent performance.

What should I do if I get this DBS-C01 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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