Question 1,068 of 1,663
How to Reduce Write Latency on Amazon RDS: Vertical Scaling
A company is running a production Amazon RDS for PostgreSQL database. The database experiences high write latency during peak hours. The company wants to reduce latency without changing the application code. Which solution is MOST cost-effective and scalable?
Quick Answer
The answer is to increase the instance size to a larger DB instance class. This vertical scaling solution directly reduces high write latency by provisioning more CPU and memory resources, which accelerates transaction processing and reduces I/O wait times for write operations. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of the trade-offs between vertical and horizontal scaling for RDS, with a common trap being the temptation to add read replicas—which only help read traffic, not write latency. The key insight is that write-heavy workloads benefit from a larger instance’s faster clock speed and larger buffer cache, not from distributing reads. For a memory tip, remember that “write latency” means you need more power in the single instance, not more copies: think “Vertical for Volume” when writes are the bottleneck.
⚠ Common exam trap
AWS often tests the misconception that Multi-AZ standby can offload writes, but in reality, the standby is a synchronous replica that does not accept write traffic and only provides failover redundancy.
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 instance size to a larger DB instance class
Increasing the instance size to a larger DB instance class directly addresses high write latency by providing more CPU and memory resources, which improves the database's ability to process write operations faster. This is the most cost-effective and scalable solution because it does not require application code changes and can be scaled vertically as needed, whereas other options either do not reduce write latency or introduce unnecessary complexity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the storage type to Provisioned IOPS (io1)
Why it's wrong here
While io1 improves IOPS, it requires application changes to fully utilize; also cost may be higher.
- ✗
Enable RDS Proxy to pool database connections
Why it's wrong here
RDS Proxy reduces connection overhead, not write latency.
- ✓
Increase the instance size to a larger DB instance class
Why this is correct
Vertical scaling can improve write throughput.
- ✗
Add a Multi-AZ standby to offload writes
Why it's wrong here
Multi-AZ standby does not offload writes; writes go to primary.
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Same concept, more angles
1 more way this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is running an Oracle database on Amazon RDS. The database has a large table that is frequently accessed by multiple applications. The DBA notices that the table has a high number of index scans but the queries are still slow. Upon investigation, the buffer cache hit ratio is low. Which design change would BEST improve performance?
hard- A.Convert the table to columnar storage using Amazon Redshift
- B.Add a read replica to offload queries
- C.Migrate the table to Amazon DynamoDB with DAX
- ✓ D.Increase the instance size to provide more memory
Why D: The low buffer cache hit ratio indicates that the database's memory (buffer cache) is insufficient to cache frequently accessed data blocks, causing excessive physical I/O. Increasing the instance size provides more memory, which expands the buffer cache and allows more data to be cached, reducing disk reads and improving query performance. This directly addresses the root cause of the slow queries despite efficient index scans.
Last reviewed: Jun 30, 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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