Quick Answer
Amazon DynamoDB with DAX is the correct choice because it delivers sub-millisecond read latency through the in-memory cache while maintaining single-digit millisecond write latency, easily handling the 10,000-character message limit within DynamoDB’s 400 KB item size, and it automatically replicates data across three Availability Zones for durability with zero operational overhead. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of when to pair a NoSQL database with a caching layer to meet extreme performance requirements, often appearing as a trap where candidates mistakenly choose ElastiCache alone or a relational database. The key distinction is that DynamoDB handles the durable, replicated storage natively, while DAX accelerates only reads—so for a real-time chat application, you need both for full sub-millisecond performance. Memory tip: “DAX for reads, DynamoDB for deeds”—the cache speeds up fetching, the database ensures messages are safely stored.
This DBS-C01 practice question tests your understanding of workload-specific database design. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 building a real-time chat application that requires storing messages with a maximum of 10,000 characters per message. The application needs sub-millisecond latency for reads and writes. The data must be durable and replicated across three Availability Zones. The development team wants to minimize operational overhead. Which AWS database service is most appropriate?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Amazon ElastiCache for Redis with replication
Why wrong: Not durable; data loss on failure.
Amazon DynamoDB with DAX
Serverless, sub-millisecond latency, durable, multi-AZ.
Amazon RDS for PostgreSQL with Multi-AZ
Why wrong: Operational overhead and higher latency.
Amazon Aurora MySQL with Multi-AZ
Why wrong: May not provide sub-millisecond latency for writes.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Amazon DynamoDB with DAX
Amazon DynamoDB with DAX is the most appropriate choice because it provides single-digit millisecond latency for reads and writes, supports up to 400 KB per item (easily accommodating 10,000 characters), and offers built-in replication across three Availability Zones for durability. DAX (DynamoDB Accelerator) further reduces read latency to sub-millisecond by serving as an in-memory cache, while DynamoDB itself handles write durability and replication automatically, minimizing operational overhead.
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.
Amazon ElastiCache for Redis with replication
Why it's wrong here
Not durable; data loss on failure.
Amazon DynamoDB with DAX
Why this is correct
Serverless, sub-millisecond latency, durable, multi-AZ.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Amazon RDS for PostgreSQL with Multi-AZ
Why it's wrong here
Operational overhead and higher latency.
Amazon Aurora MySQL with Multi-AZ
Why it's wrong here
May not provide sub-millisecond latency for writes.
Common exam traps
The trap here is that candidates often choose ElastiCache for Redis (Option A) because of its sub-millisecond latency, overlooking the requirement for durable, multi-AZ replicated storage that Redis alone does not provide natively without additional configuration and operational overhead.
Detailed technical explanation
DynamoDB uses SSD-backed storage and a distributed hash table to achieve consistent low-latency performance, with DAX acting as a write-through cache that offloads read traffic from the main table. The 10,000-character message (approximately 10 KB) is well within DynamoDB's 400 KB item size limit, and the service automatically replicates data across three AZs using synchronous replication to ensure durability. In real-world scenarios, DynamoDB's adaptive capacity and auto-scaling allow it to handle sudden spikes in chat traffic without manual intervention, whereas relational databases would require read replicas or sharding to achieve similar throughput.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
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FAQ
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
The correct answer is: Amazon DynamoDB with DAX — Amazon DynamoDB with DAX is the most appropriate choice because it provides single-digit millisecond latency for reads and writes, supports up to 400 KB per item (easily accommodating 10,000 characters), and offers built-in replication across three Availability Zones for durability. DAX (DynamoDB Accelerator) further reduces read latency to sub-millisecond by serving as an in-memory cache, while DynamoDB itself handles write durability and replication automatically, minimizing operational overhead.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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