DEA-C01 Data Store Management Practice Question
A data engineer manages an Amazon DynamoDB table that stores IoT sensor readings. The table uses a partition key of deviceId and a sort key of timestamp, with a provisioned read capacity of 100 RCUs. During a sudden spike in traffic, the engineer observes throttling on read operations even though the consumed read capacity is well below the provisioned limit. What is the MOST likely cause of the throttling?
⚠ Common exam trap
The trap here is assuming that throttling always means total provisioned capacity is insufficient, overlooking partition-level limits.
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
✓
The table's partition key is a low-cardinality attribute, causing a hot partition.
DynamoDB throttling can occur even when total consumed capacity is below the provisioned level if reads are concentrated on a few partitions. Each partition has a maximum throughput of 3,000 RCUs. A low-cardinality partition key creates hot partitions, causing localized throttling. The solution is to use a higher-cardinality partition key or add a write sharding strategy.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The table uses eventually consistent reads, which are throttled more aggressively than strongly consistent reads.
Why it's wrong here
Eventually consistent reads consume half the RCUs of strongly consistent reads and are not throttled more aggressively. In fact, they are less likely to cause capacity issues because they use fewer resources. The throttling is due to partition-level limits, not the consistency model chosen.
- ✗
The provisioned read capacity is set too low for the table's data volume.
Why it's wrong here
The scenario states that consumed read capacity is well below the provisioned limit, so the total capacity is sufficient. Throttling occurs even when aggregate usage is low, indicating a localized capacity issue rather than an overall shortage. Increasing provisioned capacity would not fix the problem and would raise costs unnecessarily.
- ✗
The table lacks a global secondary index (GSI) on the timestamp attribute.
Why it's wrong here
A GSI is used to enable queries on non-key attributes, but its absence does not cause throttling on the base table. Throttling here is due to uneven read distribution across partitions, not missing indexing. Adding a GSI would not resolve the hot partition issue and could introduce additional capacity costs.
- ✓
The table's partition key is a low-cardinality attribute, causing a hot partition.
Why this is correct
A low-cardinality partition key, such as deviceId with few unique values, concentrates read traffic on a small number of partitions. DynamoDB limits each partition to 3,000 RCUs, so even if total consumed capacity is under 100 RCUs, a single partition can exceed its local limit and throttle requests. This matches the symptom of throttling despite low aggregate usage.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
This DEA-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 DEA-C01 exam.