Quick Answer
The answer is to increase the instance size (memory and CPU) of the cross-Region read replica. This is the most effective action because replica lag in RDS for PostgreSQL is typically caused by the replica’s inability to replay the incoming write-ahead log (WAL) data fast enough; a larger instance provides the additional compute and memory resources needed to apply those changes more quickly, directly resolving the bottleneck on the replica side without affecting the primary. On the AWS Certified Data Engineer Associate DEA-C01 exam, this question tests your understanding of cross-region replication mechanics and the common misconception that you must scale the primary—when in fact, lag is almost always a replica-side resource constraint. A useful memory tip: think of the replica as a “WAL player”—if it’s too slow to replay the tape, give it a faster engine, not a bigger source.
This DEA-C01 practice question tests your understanding of data store management. 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 runs an Amazon RDS for PostgreSQL database. To meet disaster recovery requirements, they set up a cross-Region read replica. The replica has been lagging by several minutes. Which action is MOST effective to reduce the replica lag?
Enable Multi-AZ on the primary database.
Why wrong: Multi-AZ provides failover, not reduce replica lag.
Increase the instance size (memory and CPU) of the replica.
A larger replica can apply changes faster.
Increase the instance size of the primary database.
Why wrong: This helps write throughput but lag is about replica apply speed.
Decrease the instance size of the replica to reduce cost.
Why wrong: Smaller replica will lag more.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Increase the instance size (memory and CPU) of the replica.
Increasing the instance size (memory and CPU) of the cross-Region read replica is the most effective action because replica lag in Amazon RDS for PostgreSQL is often caused by the replica being unable to keep up with the volume of write-ahead log (WAL) data arriving from the primary. A larger replica instance provides more compute and memory resources to apply WAL changes faster, reducing the replay lag. This directly addresses the bottleneck at the replica side without impacting the primary database.
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.
Enable Multi-AZ on the primary database.
Why it's wrong here
Multi-AZ provides failover, not reduce replica lag.
Increase the instance size (memory and CPU) of the replica.
Why this is correct
A larger replica can apply changes faster.
Related concept
Read the scenario before looking for a memorised answer.
Increase the instance size of the primary database.
Why it's wrong here
This helps write throughput but lag is about replica apply speed.
Decrease the instance size of the replica to reduce cost.
Why it's wrong here
Smaller replica will lag more.
Common exam traps
The trap here is that candidates often assume the primary database is the bottleneck and choose to scale it up, but the lag is caused by the replica's inability to apply changes quickly enough, making the replica's instance size the correct lever to adjust.
Detailed technical explanation
In Amazon RDS for PostgreSQL, cross-Region read replicas use asynchronous replication based on streaming WAL data. The replica lag metric measures the time difference between the last WAL write on the primary and the last WAL apply on the replica. Under the hood, the replica's apply process (startup process) is single-threaded for WAL replay in PostgreSQL, so increasing CPU and memory can help by allowing more efficient caching and faster I/O, but in extreme cases, using logical replication or partitioning the workload may be needed to further reduce lag.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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FAQ
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
The correct answer is: Increase the instance size (memory and CPU) of the replica. — Increasing the instance size (memory and CPU) of the cross-Region read replica is the most effective action because replica lag in Amazon RDS for PostgreSQL is often caused by the replica being unable to keep up with the volume of write-ahead log (WAL) data arriving from the primary. A larger replica instance provides more compute and memory resources to apply WAL changes faster, reducing the replay lag. This directly addresses the bottleneck at the replica side without impacting the primary database.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This DEA-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 DEA-C01 exam.
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