- A
Disable synchronous commit on the primary to reduce log generation
Why wrong: Disabling synchronous commit can lead to data loss in case of a crash.
- B
Change the standby instance to a larger instance type (e.g., db.r5.2xlarge) to improve apply throughput
Why wrong: The bottleneck is I/O, not CPU/memory; increasing instance size may not help.
- C
Reduce the batch write frequency to every 10 minutes to lower the log generation rate
Why wrong: This would affect the application's data freshness requirements.
- D
Increase the Provisioned IOPS on both the primary and standby instances to improve log write throughput
Higher IOPS reduces the time to flush transaction logs, reducing replica lag.
Question 1,021 of 1,730
DBS-C01 Replica Lag 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. A key principle to apply: replica Lag. 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 company runs a critical application on Amazon RDS for PostgreSQL with Multi-AZ deployment. The database is a db.r5.xlarge instance with 500 GB of Provisioned IOPS (io1) storage. The application writes a large volume of time-series data every 5 minutes. Recently, the team noticed that the replica lag between the primary and standby instance has increased to over 10 seconds during peak write periods. The application requires that the standby be within 5 seconds of the primary for disaster recovery purposes. The team has already verified that network latency between AZs is minimal, and the standby instance is the same size as the primary. The CloudWatch metric 'TransactionLogsDiskUsage' shows that the primary is generating logs at a high rate. Which combination of actions should the database administrator take to reduce the replica lag? (Choose the best option.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue:
"primary"Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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
✓
Increase the Provisioned IOPS on both the primary and standby instances to improve log write throughput
The correct answer is D. Increasing Provisioned IOPS on both the primary and standby instances improves I/O throughput for writing transaction logs, which is the bottleneck causing replica lag. Higher IOPS reduces the time needed to generate logs on the primary and apply them on the standby. Option A is incorrect because disabling synchronous commit would reduce durability and may still not achieve the required lag reduction. Option B is incorrect since the standby instance size is already equal to the primary; the issue is I/O performance, not compute capacity. Option C is incorrect because reducing batch frequency impacts application responsiveness and does not address the I/O bottleneck.
Key principle: Replica Lag
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable synchronous commit on the primary to reduce log generation
Why it's wrong here
Disabling synchronous commit can lead to data loss in case of a crash.
- ✗
Change the standby instance to a larger instance type (e.g., db.r5.2xlarge) to improve apply throughput
Why it's wrong here
The bottleneck is I/O, not CPU/memory; increasing instance size may not help.
- ✗
Reduce the batch write frequency to every 10 minutes to lower the log generation rate
Why it's wrong here
This would affect the application's data freshness requirements.
- ✓
Increase the Provisioned IOPS on both the primary and standby instances to improve log write throughput
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Replica Lag
- Provisioned IOPS
- Transaction Logs
- Multi-AZ
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
Replica Lag
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.
Review replica Lag, then practise related DBS-C01 questions on the same topic to reinforce the concept.
- →
Monitoring and Troubleshooting — study guide chapter
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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 — Replica Lag.
What is the correct answer to this question?
The correct answer is: Increase the Provisioned IOPS on both the primary and standby instances to improve log write throughput — The correct answer is D. Increasing Provisioned IOPS on both the primary and standby instances improves I/O throughput for writing transaction logs, which is the bottleneck causing replica lag. Higher IOPS reduces the time needed to generate logs on the primary and apply them on the standby. Option A is incorrect because disabling synchronous commit would reduce durability and may still not achieve the required lag reduction. Option B is incorrect since the standby instance size is already equal to the primary; the issue is I/O performance, not compute capacity. Option C is incorrect because reducing batch frequency impacts application responsiveness and does not address the I/O bottleneck.
What should I do if I get this DBS-C01 question wrong?
Review replica Lag, then practise related DBS-C01 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "best", "primary". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Replica Lag
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Last reviewed: Jun 20, 2026
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