DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. 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.
Exhibit
Refer to the exhibit.
```json
{
"MemoryReservation": {
"Value": 500
},
"MemoryUsage": {
"Value": 450
},
"ActiveTransactions": {
"Value": 20
},
"DatabaseConnections": {
"Value": 100
},
"ReadIOPS": {
"Value": 5000
},
"WriteIOPS": {
"Value": 2000
},
"ReadLatency": {
"Value": 2.5
},
"WriteLatency": {
"Value": 5.0
}
}
```
The exhibit shows CloudWatch metrics from an Amazon RDS for PostgreSQL instance (db.r5.large, 16 GB memory, 5000 provisioned IOPS). The application is experiencing slow query performance.
Refer to the exhibit. The exhibit shows CloudWatch metrics from an Amazon RDS for PostgreSQL instance. The application is experiencing slow query performance. Which is the most likely cause?
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.
Exhibit
Refer to the exhibit.
```json
{
"MemoryReservation": {
"Value": 500
},
"MemoryUsage": {
"Value": 450
},
"ActiveTransactions": {
"Value": 20
},
"DatabaseConnections": {
"Value": 100
},
"ReadIOPS": {
"Value": 5000
},
"WriteIOPS": {
"Value": 2000
},
"ReadLatency": {
"Value": 2.5
},
"WriteLatency": {
"Value": 5.0
}
}
```
The exhibit shows CloudWatch metrics from an Amazon RDS for PostgreSQL instance (db.r5.large, 16 GB memory, 5000 provisioned IOPS). The application is experiencing slow query performance.
A
High storage latency due to provisioned IOPS being fully utilized or EBS volume contention
Read/Write latency significantly above expected values for provisioned IOPS storage.
B
High CPU utilization due to complex queries
Why wrong: CPU metrics not shown, but latency is more likely storage-related.
C
Too many database connections causing context switching
Why wrong: 100 connections is not excessive for db.r5.large.
D
Insufficient memory causing disk swaps
Why wrong: Memory usage is 450 MB, far below 16 GB.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
High storage latency due to provisioned IOPS being fully utilized or EBS volume contention
The exhibit shows that the 'Write IOPS' metric is consistently at or near the provisioned IOPS limit, while 'Write Latency' is elevated. When provisioned IOPS are fully utilized, Amazon EBS throttles I/O, causing increased storage latency. This directly degrades query performance for PostgreSQL, especially for write-heavy workloads, as each write operation must wait for the storage layer to complete.
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.
✓
High storage latency due to provisioned IOPS being fully utilized or EBS volume contention
Why this is correct
Read/Write latency significantly above expected values for provisioned IOPS storage.
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.
✗
High CPU utilization due to complex queries
Why it's wrong here
CPU metrics not shown, but latency is more likely storage-related.
✗
Too many database connections causing context switching
Why it's wrong here
100 connections is not excessive for db.r5.large.
✗
Insufficient memory causing disk swaps
Why it's wrong here
Memory usage is 450 MB, far below 16 GB.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see high latency and assume a memory or CPU bottleneck, but the key clue is the IOPS metric hitting its provisioned ceiling, which directly points to storage I/O throttling as the root cause.
Trap categories for this question
Command / output trap
CPU metrics not shown, but latency is more likely storage-related.
Detailed technical explanation
How to think about this question
Amazon RDS for PostgreSQL on EBS-backed storage uses a credit-based I/O model for gp2 volumes or a provisioned IOPS model for io1/io2. When write IOPS exceed the provisioned limit, EBS throttles requests, introducing queue depth and increased latency. This is visible in CloudWatch as 'WriteIOPS' hitting a plateau and 'WriteLatency' spiking. The database may still show low CPU and memory, misleading engineers into thinking the issue is elsewhere.
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.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: High storage latency due to provisioned IOPS being fully utilized or EBS volume contention — The exhibit shows that the 'Write IOPS' metric is consistently at or near the provisioned IOPS limit, while 'Write Latency' is elevated. When provisioned IOPS are fully utilized, Amazon EBS throttles I/O, causing increased storage latency. This directly degrades query performance for PostgreSQL, especially for write-heavy workloads, as each write operation must wait for the storage layer to complete.
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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Question Discussion
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