DBS-C01 Hot Partition Practice Question
A company is using Amazon DynamoDB as the primary database for a global e-commerce application. During the holiday season, the application experiences throttling on write requests even though the read and write capacity units are well below the provisioned limits. The table uses on-demand capacity mode. What is the most likely cause of this throttling?
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
✓
There is a hot partition due to an uneven write distribution across partition keys.
In DynamoDB on-demand capacity mode, throughput scales automatically based on traffic. However, throttling can still occur if a single partition receives more write requests than the partition's maximum throughput capacity (1,000 WCU per partition). This is known as a hot partition, caused by an uneven distribution of write activity across partition keys. Option A correctly identifies this. Option B is incorrect because on-demand mode does not use provisioned capacity. Option C uses incorrect terminology—there is no 'maximum write capacity units per partition' that the table as a whole can exceed. Option D is incorrect because DynamoDB does not have a per-region account-level write limit that causes throttling on a single table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
There is a hot partition due to an uneven write distribution across partition keys.
Why this is correct
Correct. Uneven write distribution creates a hot partition that exceeds the partition's throughput limit, causing throttling even in on-demand mode.
- ✗
The table's provisioned write capacity is set too low.
Why it's wrong here
Incorrect. The table uses on-demand capacity mode, so there is no provisioned write capacity to set too low.
- ✗
The table has exceeded the maximum write capacity units per partition.
Why it's wrong here
Incorrect. While each partition has a maximum capacity (1,000 WCU), this option inaccurately describes the issue as a table-level limit rather than a single partition limitation.
- ✗
The AWS account has reached the DynamoDB write throughput limit per region.
Why it's wrong here
Incorrect. AWS accounts do not have a regional write throughput limit for DynamoDB that would throttle a single table.
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Same concept, more angles
1 more way this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An organization is using Amazon DynamoDB with on-demand capacity. They notice that the 'ThrottledRequests' metric is non-zero during a specific hour each day. The table stores session data and has a partition key of 'user_id'. The workload is uniform. What is the most likely cause of throttling?
medium- A.The table has on-demand capacity and cannot throttle.
- ✓ B.The account-level read/write capacity limit is exceeded.
- C.A global secondary index is consuming write capacity.
- D.The partition key is not evenly distributed.
Why B: With on-demand capacity, throttling can occur when the account-level read/write capacity limit is exceeded, even with a uniform workload. The account-level limit (default 40,000 RCU or 40,000 WCU) applies across all on-demand tables in an AWS account. If the workload spikes during a specific hour, it may exceed this limit, causing throttling. Although per-partition limits exist (3,000 RCU or 1,000 WCU), a uniform workload means partition key distribution is even, so hot partitions are unlikely. Thus, the most likely cause is the account-level limit being reached.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.