Question 459 of 247
SOA-C02 Cost and Performance Optimization Practice Question
A company runs a read-heavy database workload on Amazon RDS for PostgreSQL with a primary instance and two read replicas. The SysOps administrator observes that the read replicas frequently experience high replica lag during peak hours, causing stale reads for the application. The administrator needs to reduce replica lag while optimizing costs. The workload is predictable, with spikes during business hours and low traffic at night. Which combination of actions should the administrator take?
⚠ Common exam trap
A common mix-up: candidates confuse replica lag with primary performance, leading them to upgrade the primary (Option D) or add more replicas (Option C), when the real bottleneck is the replica's WAL replay capacity.
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
✓
Upgrade the instance class of the read replicas to a larger type with more CPU and memory to handle the increased WAL replay rate.
Upgrading the read replica instance class provides more CPU and memory, which directly increases the WAL replay rate. In RDS for PostgreSQL, replica lag is primarily caused by the replica's inability to apply WAL changes as fast as the primary generates them. A larger instance class alleviates this bottleneck without incurring the cost of upgrading the primary instance.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Convert the read replicas to Multi-AZ instances to improve the replication process and reduce lag.
Why it's wrong here
Multi-AZ for read replicas provides standby replicas for failover, but it does not reduce replica lag. In fact, running Multi-AZ adds overhead because the primary in the replica's AZ must also replicate to the standby.
- ✓
Upgrade the instance class of the read replicas to a larger type with more CPU and memory to handle the increased WAL replay rate.
Why this is correct
Replica lag occurs when the replica cannot keep up with the rate of changes from the primary. Increasing the replica's instance size gives it more resources to apply WAL data faster, reducing lag. This directly addresses the performance bottleneck.
- ✗
Add additional read replicas to distribute the read load and reduce the lag on each individual replica.
Why it's wrong here
Adding more replicas does not reduce the lag on existing replicas; it may increase the load on the primary because it must stream the WAL to more replicas, potentially worsening the lag. The solution is to make each replica more powerful.
- ✗
Upgrade the primary DB instance to a larger class with increased IOPS to reduce the amount of data that needs to be replicated.
Why it's wrong here
While upgrading the primary could improve overall throughput, the replica lag is specifically caused by the replicas' inability to apply changes quickly. The replicas are the bottleneck. Upgrading the primary is less cost-effective and may not solve the lag issue.
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Last reviewed: Jun 11, 2026
This SOA-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 SOA-C02 exam.
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