- A
Use only player ID as row key with column qualifiers for timestamps.
Why wrong: Single row per player will be too wide and cause hotspotting on popular players.
- B
Use a row key of player ID followed by reversed timestamp.
Player ID distributes writes across tablets; reversed timestamp makes recent data appear at the start of the range for efficient scans.
- C
Prefix with timestamp and append player ID.
Why wrong: Prefixing with timestamp causes all writes to go to the same tablet at a given time, creating hotspots.
- D
Use a hash of player ID as row key and store timestamps in cell versions.
Why wrong: Hashing distributes writes but loses natural ordering, making time range scans inefficient.
Question 100 of 1,000
PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 game company uses Cloud Bigtable to store player session data. Access patterns include looking up a player's most recent sessions and scanning sessions by time range. Which row key design is most appropriate?
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 row key of player ID followed by reversed timestamp.
Option B is correct because it leverages Cloud Bigtable's sorted row key structure to group all sessions for a given player ID together, while the reversed timestamp ensures that the most recent session appears first within that group. This design enables efficient point lookups for a player's latest sessions and supports range scans over time ranges by using the timestamp portion of the key.
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 only player ID as row key with column qualifiers for timestamps.
Why it's wrong here
Single row per player will be too wide and cause hotspotting on popular players.
- ✓
Use a row key of player ID followed by reversed timestamp.
Why this is correct
Player ID distributes writes across tablets; reversed timestamp makes recent data appear at the start of the range for efficient scans.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Prefix with timestamp and append player ID.
Why it's wrong here
Prefixing with timestamp causes all writes to go to the same tablet at a given time, creating hotspots.
- ✗
Use a hash of player ID as row key and store timestamps in cell versions.
Why it's wrong here
Hashing distributes writes but loses natural ordering, making time range scans inefficient.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think hashing or using timestamps as a prefix will distribute load evenly, but they overlook that the primary access pattern requires grouping by player ID and ordering by time, which the reversed timestamp suffix elegantly satisfies.
Detailed technical explanation
How to think about this question
Cloud Bigtable stores rows in lexicographic order of row keys, so a key like 'playerID#<reversed_timestamp>' places all rows for the same player contiguously, and the reversed timestamp (e.g., 9223372036854775807 - epoch_millis) ensures the most recent entry is read first. This design also supports time-range scans by using a start and end key that bracket the desired timestamp range within the player's key space, leveraging Bigtable's built-in prefix scan optimization.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
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FAQ
Questions learners often ask
What does this PCDE question test?
Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a row key of player ID followed by reversed timestamp. — Option B is correct because it leverages Cloud Bigtable's sorted row key structure to group all sessions for a given player ID together, while the reversed timestamp ensures that the most recent session appears first within that group. This design enables efficient point lookups for a player's latest sessions and supports range scans over time ranges by using the timestamp portion of the key.
What should I do if I get this PCDE 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.
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Last reviewed: Jul 4, 2026
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