- A
Use the user ID as the only row key and store timestamps as column qualifiers.
Why wrong: This would require scanning all columns for each user, inefficient for time-range queries.
- B
Use a monotonically increasing integer as the row key.
Why wrong: Monotonically increasing keys can cause hotspots and do not prioritize recent data.
- C
Reverse the timestamp and place it at the beginning of the row key (e.g., 2024-01-15T10:30:00_rev#user123).
Reversed timestamp at the start allows scanning the most recent data first.
- D
Use a hash of the user ID as a prefix (salting) to distribute writes evenly.
Why wrong: Salting helps write distribution but does not optimize queries for recent data.
Question 564 of 1,000
PCDOE Design and Plan Database Solutions Practice Question
This PCDOE practice question tests your understanding of design and plan 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.
A company uses Bigtable for time-series analytics and needs to query the most recent data points first. The row key currently consists of a user ID followed by a timestamp (e.g., user123#2024-01-15T10:30:00). However, frequent queries filter by time range across all users. Which row key design change would optimize query performance for this access pattern?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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
✓
Reverse the timestamp and place it at the beginning of the row key (e.g., 2024-01-15T10:30:00_rev#user123).
Option C is correct because reversing the timestamp and placing it at the beginning of the row key ensures that the most recent data points are stored first in lexicographic order. Bigtable stores rows sorted by row key, so queries filtering by a time range across all users can now scan a contiguous range of rows without needing to skip over user ID prefixes. This design avoids the hotspotting and inefficient scans that occur when the timestamp is not the leading part of the key for time-range queries.
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 the user ID as the only row key and store timestamps as column qualifiers.
Why it's wrong here
This would require scanning all columns for each user, inefficient for time-range queries.
- ✗
Use a monotonically increasing integer as the row key.
Why it's wrong here
Monotonically increasing keys can cause hotspots and do not prioritize recent data.
- ✓
Reverse the timestamp and place it at the beginning of the row key (e.g., 2024-01-15T10:30:00_rev#user123).
Why this is correct
Reversed timestamp at the start allows scanning the most recent data first.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a hash of the user ID as a prefix (salting) to distribute writes evenly.
Why it's wrong here
Salting helps write distribution but does not optimize queries for recent data.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that salting or hashing is always the best solution for Bigtable row key design, but candidates must recognize that for time-range queries across all users, the row key must be ordered by time first to enable efficient range scans.
Detailed technical explanation
How to think about this question
Bigtable stores rows in lexicographic order by row key, and a reversed timestamp (e.g., using a high-precision time minus the timestamp) ensures that recent data appears at the beginning of the sorted order. This design allows time-range scans to read a contiguous block of rows, which is critical for low-latency analytics. In practice, the reversed timestamp can be implemented as (Long.MAX_VALUE - timestamp) to maintain monotonic ordering, and combining it with a user ID suffix still allows per-user queries if needed.
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 PCDOE question test?
Design and Plan Database Solutions — This question tests Design and Plan Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Reverse the timestamp and place it at the beginning of the row key (e.g., 2024-01-15T10:30:00_rev#user123). — Option C is correct because reversing the timestamp and placing it at the beginning of the row key ensures that the most recent data points are stored first in lexicographic order. Bigtable stores rows sorted by row key, so queries filtering by a time range across all users can now scan a contiguous range of rows without needing to skip over user ID prefixes. This design avoids the hotspotting and inefficient scans that occur when the timestamp is not the leading part of the key for time-range queries.
What should I do if I get this PCDOE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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 PCDOE 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 PCDOE exam.
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