AWS Certified Solutions Architect Associate SAA-C03 Practice Question
An application uses Amazon DynamoDB in provisioned-capacity mode and experiences periodic read bursts that are beginning to push the table close to its maximum provisioned read capacity. A solutions architect is evaluating whether introducing Amazon DynamoDB Accelerator (DAX) in front of the table will lower the overall monthly cost.
Which ONE of the following factors is MOST critical in determining whether adding DAX will actually produce a net cost saving?
Whether the application requires strongly consistent reads.
Whether DynamoDB Streams are enabled on the table.
The average size (in kilobytes) of items stored in the DynamoDB table.
The cache-hit ratio that the workload is expected to achieve when DAX is introduced.
To achieve cost savings with DAX, the workload must achieve a high cache-hit ratio so that the reduction in DynamoDB read requests (and the associated RCU charges) outweighs the hourly cost of running the DAX cluster. AWS documentation states that with a high hit rate, the decrease in table read cost can exceed the cost of the DAX nodes, resulting in a net saving. If the hit ratio is low-or if the workload is predominantly write-heavy-DAX may increase total cost.
Other factors (item size, DynamoDB Streams, strong consistency requirements) affect design choices, but they do not directly determine whether DAX will reduce cost.
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