- A
Use a hash of the user_id as the prefix
Salting with a hash is also a valid technique, but the question expects one answer. Reversing the key is more common and directly addresses the issue. However, since both could be correct, the best answer is A.
- B
Use a single table with no row key change
Why wrong: Keeping the same design will continue to cause hotspots.
- C
Increase the number of nodes to 20
Why wrong: Adding nodes may not solve the hotspot if the row key design is poor; the single node will still be overloaded.
- D
Use a composite key: timestamp + user_id
By placing the timestamp first, writes are distributed across nodes because timestamps are monotonically increasing but spread over time. This avoids the hotspot caused by UUID prefix.
Question 962 of 980
PCD Practice Question: Design Scalable and Highly Available Cloud Database Solutions
This PCD practice question tests your understanding of design scalable and highly available cloud database solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A DevOps engineer is designing a row key for a Bigtable table storing user activity logs. The pattern is: user_id (UUID) + timestamp. On a cluster with 10 nodes, they observe severe hotspotting on a single node during peak writes. Which row key design change would likely resolve this issue?
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 a hash of the user_id as the prefix
Option A is correct because prepending a hash of the user_id distributes writes uniformly across all Bigtable tablets. Bigtable uses the row key prefix to determine tablet assignment; a UUID prefix is random but sequential UUIDs (e.g., time-based) can cluster writes. A hash function (e.g., MD5 or CRC32) ensures even distribution, eliminating hotspotting on a single node.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 a hash of the user_id as the prefix
Why this is correct
Salting with a hash is also a valid technique, but the question expects one answer. Reversing the key is more common and directly addresses the issue. However, since both could be correct, the best answer is A.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a single table with no row key change
Why it's wrong here
Keeping the same design will continue to cause hotspots.
- ✗
Increase the number of nodes to 20
Why it's wrong here
Adding nodes may not solve the hotspot if the row key design is poor; the single node will still be overloaded.
- ✓
Use a composite key: timestamp + user_id
Why this is correct
By placing the timestamp first, writes are distributed across nodes because timestamps are monotonically increasing but spread over time. This avoids the hotspot caused by UUID prefix.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that reversing the key order (timestamp + user_id) improves distribution, but in reality it creates a hotspot on the tablet handling the current timestamp range.
Detailed technical explanation
How to think about this question
Bigtable splits tablets by row key range; a monotonically increasing prefix (like timestamp) creates a 'hot row' where all new writes land on the last tablet. Hashing the user_id (e.g., using a 4-byte hash prefix) scatters writes across the entire key space, leveraging Bigtable's automatic load balancing. In practice, a common pattern is to use a hash of the user_id as the first 4 bytes, then append the timestamp for range scans within a user's activity.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this PCD question test?
Design Scalable and Highly Available Cloud Database Solutions — This question tests Design Scalable and Highly Available Cloud Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a hash of the user_id as the prefix — Option A is correct because prepending a hash of the user_id distributes writes uniformly across all Bigtable tablets. Bigtable uses the row key prefix to determine tablet assignment; a UUID prefix is random but sequential UUIDs (e.g., time-based) can cluster writes. A hash function (e.g., MD5 or CRC32) ensures even distribution, eliminating hotspotting on a single node.
What should I do if I get this PCD question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jul 4, 2026
This PCD practice question is part of Courseiva's free Google Cloud 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 PCD exam.
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