Quick Answer
The answer is the ReplicaLag metric. This metric directly measures the time in seconds between the primary RDS instance applying a change and the read replica applying that same change, making it the definitive indicator of how far behind a replica has fallen. For the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding that while other metrics like DiskQueueDepth or ReadLatency relate to performance, only ReplicaLag specifically tracks synchronization delay between the primary and its read replicas. A common trap is confusing storage or I/O metrics with replication health, so remember that lag is about data currency, not throughput. Memory tip: think "Lag equals Lagging behind" — if you see any other metric name, it’s likely a distractor focused on hardware or latency, not sync status.
This DBS-C01 practice question tests your understanding of management and operations. 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 company is using Amazon RDS for PostgreSQL with read replicas to offload read traffic. The company wants to ensure that the read replicas are always in sync with the primary instance. Which metric should the company monitor to detect replication lag?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
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.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
DiskQueueDepth
Why wrong: This metric measures the number of I/O operations waiting to be processed, not replication lag.
ReplicaLag
This metric shows the time difference between the primary and replica in seconds.
TransactionLogsDiskUsage
Why wrong: This metric is not provided by RDS.
ReadLatency
Why wrong: This measures the time for read operations, not replication lag.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ReplicaLag
RDS provides the ReplicaLag metric in CloudWatch for PostgreSQL read replicas. Option A (DiskQueueDepth) is for storage. Option B (ReadLatency) is for read operations. Option D (TransactionLogsDiskUsage) is not a standard metric.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DiskQueueDepth
ReplicaLag
Why this is correct
This metric shows the time difference between the primary and replica in seconds.
Clue confirmation
The clue words "primary", "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
TransactionLogsDiskUsage
Why it's wrong here
This metric is not provided by RDS.
ReadLatency
Why it's wrong here
This measures the time for read operations, not replication lag.
Common exam traps
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
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which DBS-C01 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.
Management and Operations — study guide chapter
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FAQ
Management and Operations — This question tests Management and Operations — Read the scenario before looking for a memorised answer..
The correct answer is: ReplicaLag — RDS provides the ReplicaLag metric in CloudWatch for PostgreSQL read replicas. Option A (DiskQueueDepth) is for storage. Option B (ReadLatency) is for read operations. Option D (TransactionLogsDiskUsage) is not a standard metric.
Identify which DBS-C01 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.
Yes — watch for: "primary", "always". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 20, 2026
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.
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