The answer is that the instance has reached the IOPS limit of the gp2 volume. A consistently high DiskQueueDepth metric, especially above 100, signals that the storage subsystem cannot process I/O requests as fast as they are arriving, causing operations to queue. For a 1000 GB gp2 volume, the baseline is 3000 IOPS (3 IOPS per GB), and once the workload exhausts the burst credit balance, performance is throttled to this baseline, leading to queued requests and an elevated DiskQueueDepth. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of gp2 burst behavior versus gp3 or io2 performance; a common trap is to blame the database engine or instance size rather than the storage layer. Remember that gp2’s burst credits are like a sprint—once spent, you’re stuck at the baseline pace. A useful memory tip: “Queue depth climbs when credits run out of time.”
DBS-C01 Monitoring and Troubleshooting Practice Question
This DBS-C01 practice question tests your understanding of monitoring and troubleshooting. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A database engineer is monitoring an Amazon RDS for PostgreSQL instance and notices that the 'DiskQueueDepth' metric is consistently above 100. The instance uses gp2 storage with 1000 GB allocated. What is the most likely cause of the high disk queue depth?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The instance has reached the IOPS limit of the gp2 volume
Option B is correct because a consistently high DiskQueueDepth (above 100) on an Amazon RDS for PostgreSQL instance with gp2 storage indicates that the volume is saturating its IOPS limit. gp2 volumes provide a baseline of 3 IOPS per GB (up to 16,000 IOPS), so a 1000 GB gp2 volume has a baseline of 3000 IOPS. When the workload exceeds this baseline, the volume relies on burst credits, and once credits are exhausted, IOPS are throttled to the baseline, causing I/O requests to queue up and the DiskQueueDepth metric to rise.
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.
✗
Replication lag between the primary and standby instance
Why it's wrong here
Replication lag measures delay in data replication, not storage I/O.
✓
The instance has reached the IOPS limit of the gp2 volume
Why this is correct
For a 1000 GB gp2 volume, baseline IOPS is 3000; sustained I/O beyond that causes queuing.
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.
✗
Insufficient memory allocated to the instance
Why it's wrong here
Memory issues cause swapping, not high disk queue depth.
✗
Network throughput limit is being exceeded
Why it's wrong here
Network limits would show in network metrics, not disk queue depth.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse DiskQueueDepth with memory or network metrics, or assume that any high queue depth automatically indicates a hardware failure, rather than recognizing it as a symptom of IOPS exhaustion on gp2 storage.
Trap categories for this question
Command / output trap
Network limits would show in network metrics, not disk queue depth.
Detailed technical explanation
How to think about this question
The DiskQueueDepth metric represents the number of pending I/O requests waiting to be serviced by the EBS volume. For gp2 volumes, the burst credit bucket allows short bursts up to 3000 IOPS for a 1000 GB volume, but sustained workloads above 3000 IOPS deplete credits, leading to throttling and queue buildup. A common real-world scenario is a batch job or heavy write workload that exceeds the baseline, causing performance degradation until the queue drains or credits replenish.
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.
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 instance has reached the IOPS limit of the gp2 volume — Option B is correct because a consistently high DiskQueueDepth (above 100) on an Amazon RDS for PostgreSQL instance with gp2 storage indicates that the volume is saturating its IOPS limit. gp2 volumes provide a baseline of 3 IOPS per GB (up to 16,000 IOPS), so a 1000 GB gp2 volume has a baseline of 3000 IOPS. When the workload exceeds this baseline, the volume relies on burst credits, and once credits are exhausted, IOPS are throttled to the baseline, causing I/O requests to queue up and the DiskQueueDepth metric to rise.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A database team is troubleshooting a performance issue on an Amazon RDS for PostgreSQL instance. They notice that the 'DiskQueueDepth' metric is consistently high. Which TWO actions should the team take to resolve this issue? (Choose TWO.)
easy
A.Increase the number of database connections.
✓ B.Enable storage auto scaling.
✓ C.Increase the provisioned IOPS for the instance.
D.Enable query caching in PostgreSQL.
E.Enable Multi-AZ deployment.
Why B: Options B and D are correct. A high disk queue depth indicates I/O bottleneck. Increasing IOPS (Option B) or enabling Auto Scaling (Option D) can alleviate the bottleneck. Option A is wrong because more connections may increase I/O contention. Option C is wrong because query caching is not a primary solution for I/O. Option E is wrong because Multi-AZ does not improve I/O performance.
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This DBS-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 DBS-C01 exam.
Question Discussion
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