- A
The primary database should be migrated to a Multi-AZ deployment instead of using a read replica.
Why wrong: Multi-AZ provides high availability, not Read scaling; replication lag can still occur.
- B
The replica's 'max_standby_streaming_delay' parameter is set too low, causing the replica to cancel queries.
Why wrong: This parameter affects query conflicts, not replication lag due to long transactions.
- C
The batch job on the primary is using long-running transactions that are holding up WAL generation.
Long transactions prevent WAL segments from being recycled and cause replication lag.
- D
The replica's instance class is still too small for the write load from the primary.
Why wrong: Increasing instance class already done; lag persists, indicating other causes.
Quick Answer
The answer is long-running transactions on the primary causing WAL generation delays. When a batch job on the primary holds a transaction open for an extended period, PostgreSQL cannot clean up old WAL segments until that transaction completes, forcing the read replica to wait for those segments before applying changes. This explains why increasing the replica’s instance class or network bandwidth fails to resolve the lag—the bottleneck is upstream at the primary’s transaction lifecycle, not downstream resources. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how replication lag stems from primary-side transaction behavior rather than replica capacity, a common trap where candidates mistakenly blame hardware. Remember the mnemonic: “Long txn, long lag”—if the primary holds a transaction open, the replica waits.
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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.
A company runs a production database on Amazon RDS for PostgreSQL. The DevOps team has set up a read replica to offload read traffic. Recently, the replica started experiencing replication lag that is increasing over time. The primary instance's CPU and memory utilization are normal. The network bandwidth between the primary and replica is not saturated. The team has already increased the replica's instance class, but the lag persists. The primary database is under heavy write load due to a batch job that runs hourly. What is the MOST likely cause of the increasing replication lag?
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.
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
The batch job on the primary is using long-running transactions that are holding up WAL generation.
Option A is correct because long-running transactions on the primary can cause replication lag because the replica must wait for the transaction to complete before applying changes. Option B is wrong because increasing replica instance class does not address the root cause. Option C is wrong because increased checkpoint timeout on the replica would not help. Option D is wrong because the issue is not related to storage type change.
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 primary database should be migrated to a Multi-AZ deployment instead of using a read replica.
Why it's wrong here
Multi-AZ provides high availability, not Read scaling; replication lag can still occur.
- ✗
The replica's 'max_standby_streaming_delay' parameter is set too low, causing the replica to cancel queries.
Why it's wrong here
This parameter affects query conflicts, not replication lag due to long transactions.
- ✓
The batch job on the primary is using long-running transactions that are holding up WAL generation.
Why this is correct
Long transactions prevent WAL segments from being recycled and cause replication lag.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The replica's instance class is still too small for the write load from the primary.
Why it's wrong here
Increasing instance class already done; lag persists, indicating other causes.
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
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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Incident and Event Response — study guide chapter
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Incident and Event Response — This question tests Incident and Event Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The batch job on the primary is using long-running transactions that are holding up WAL generation. — Option A is correct because long-running transactions on the primary can cause replication lag because the replica must wait for the transaction to complete before applying changes. Option B is wrong because increasing replica instance class does not address the root cause. Option C is wrong because increased checkpoint timeout on the replica would not help. Option D is wrong because the issue is not related to storage type change.
What should I do if I get this DOP-C02 question wrong?
Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "primary". 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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Last reviewed: Jun 20, 2026
This DOP-C02 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 DOP-C02 exam.
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