- A
Use monotonically increasing integers as the row key
Why wrong: Monotonically increasing keys cause hotspots on the last tablet server.
- B
Use field promotion to place high-cardinality fields first
Field promotion ensures even distribution by using high-cardinality field as the first part of the row key.
- C
Use a reversed timestamp as the first component
Why wrong: Reversed timestamps can still cause hotspots if not combined with other techniques; alone not sufficient.
- D
Use a hash prefix (salted key) to distribute writes
Salting adds a random prefix to spread writes across tablet servers.
- E
Use a low-cardinality field as the row key prefix
Why wrong: Low-cardinality prefixes concentrate writes on few tablets.
Question 276 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. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
You are designing a Bigtable data model for an ad-tech platform that tracks user impressions. Which TWO row key design practices should you implement to avoid hotspots and ensure even distribution?
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 field promotion to place high-cardinality fields first
Option B is correct because field promotion places the highest-cardinality field first in the row key, which spreads writes across many tablet servers. In Bigtable, rows are sorted lexicographically by row key, so a high-cardinality prefix ensures that successive writes do not concentrate on a single tablet, avoiding hotspots.
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 monotonically increasing integers as the row key
Why it's wrong here
Monotonically increasing keys cause hotspots on the last tablet server.
- ✓
Use field promotion to place high-cardinality fields first
Why this is correct
Field promotion ensures even distribution by using high-cardinality field as the first part of the row key.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a reversed timestamp as the first component
Why it's wrong here
Reversed timestamps can still cause hotspots if not combined with other techniques; alone not sufficient.
- ✓
Use a hash prefix (salted key) to distribute writes
Why this is correct
Salting adds a random prefix to spread writes across tablet servers.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a low-cardinality field as the row key prefix
Why it's wrong here
Low-cardinality prefixes concentrate writes on few tablets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that monotonically increasing keys are acceptable for Bigtable, when in fact they cause severe hotspots; candidates must remember that Bigtable's sorted storage requires random or high-cardinality prefixes for even distribution.
Detailed technical explanation
How to think about this question
Bigtable splits rows into tablets by key ranges; a hash prefix (salted key) as in option D distributes writes uniformly across tablets by randomizing the first byte. Field promotion works by ordering key components so that the most unique value comes first, which naturally spreads load without requiring a separate hash function. In practice, combining a hash prefix with a high-cardinality field is a common pattern for write-heavy workloads like ad impression tracking.
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.
What to study next
Got this wrong? Here's your next step.
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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 field promotion to place high-cardinality fields first — Option B is correct because field promotion places the highest-cardinality field first in the row key, which spreads writes across many tablet servers. In Bigtable, rows are sorted lexicographically by row key, so a high-cardinality prefix ensures that successive writes do not concentrate on a single tablet, avoiding hotspots.
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
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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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