SAP-C02 Design for New Solutions Practice Question

A company is designing a new application that will use Amazon DynamoDB as its primary database. The application has two access patterns: one requires strongly consistent reads, and the other requires eventually consistent reads. The company wants to minimize costs while meeting the read consistency requirements. How should the company configure DynamoDB reads?

⚠ Common exam trap

Many candidates assume DAX can provide strong consistency (it cannot) or that global tables are a solution for local consistency requirements, when in fact the correct approach is to use the native DynamoDB `ConsistentRead` parameter selectively based on the access pattern.

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

✓

Use strongly consistent reads for the pattern that requires it, and eventually consistent reads for the other pattern.

DynamoDB supports both strongly consistent reads and eventually consistent reads at the API level (via the `ConsistentRead` parameter). Strongly consistent reads return the most up-to-date data but consume twice the read capacity units (RCUs) compared to eventually consistent reads. By using strongly consistent reads only for the access pattern that requires it, and eventually consistent reads for the other pattern, the company minimizes RCU consumption and thus costs while meeting the specific consistency requirements of each pattern.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Use strongly consistent reads for all read requests to ensure data accuracy.
Why it's wrong here
Strongly consistent reads consume twice the read capacity units of eventually consistent reads, doubling cost for the access pattern that does not require them, contradicting the cost-minimisation goal. Applying strong consistency everywhere is tempting when accuracy is prioritised, and would be correct if every read genuinely needed it.
✗
Use DynamoDB Accelerator (DAX) to cache reads and achieve strong consistency.
Why it's wrong here
DAX serves eventually consistent reads only; it cannot satisfy a strongly consistent access pattern, so that requirement would fail. It is tempting because DAX cuts read costs and latency for read-heavy workloads, and would be the right choice if every access pattern tolerated eventual consistency.
✗
Use DynamoDB global tables with strongly consistent reads enabled.
Why it's wrong here
Global tables replicate across Regions and support only eventually consistent reads; they cannot deliver the strongly consistent access pattern required. They are tempting for multi-Region, low-latency active-active designs, and would be correct if the workload needed cross-Region replication rather than mixed read consistency.
✓
Use strongly consistent reads for the pattern that requires it, and eventually consistent reads for the other pattern.
Why this is correct
DynamoDB charges double read capacity units for strongly consistent reads, so applying them only to the pattern requiring them and eventually consistent reads elsewhere minimises cost while meeting both consistency requirements. Using strongly consistent reads for both patterns would needlessly double capacity consumption.

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SAP-C02 Design for New Solutions Practice Question

Why each option matters

Option-by-option breakdown

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