AWS Certified Database – Specialty — Question 127

An online advertising website uses an Amazon DynamoDB table with on-demand capacity mode as its data store. The website also has a DynamoDB Accelerator
(DAX) cluster in the same VPC as its web application server. The application needs to perform infrequent writes and many strongly consistent reads from the data store by querying the DAX cluster.
During a performance audit, a systems administrator notices that the application can look up items by using the DAX cluster. However, the QueryCacheHits metric for the DAX cluster consistently shows 0 while the QueryCacheMisses metric continuously keeps growing in Amazon CloudWatch.
What is the MOST likely reason for this occurrence?

Answer options

• A. A VPC endpoint was not added to access DynamoDB.
• B. Strongly consistent reads are always passed through DAX to DynamoDB.
• C. DynamoDB is scaling due to a burst in traffic, resulting in degraded performance.
• D. A VPC endpoint was not added to access CloudWatch.

Correct answer: B

Explanation

The correct answer is B because strongly consistent reads cannot be served from the DAX cache and must always go to DynamoDB, resulting in QueryCacheHits remaining at 0. The other options are incorrect as they do not accurately describe the behavior of DAX with respect to strongly consistent reads or the other services mentioned.