- A
Use customer ID + order ID as the row key (e.g., cust123#ord456).
This enables efficient scans by customer ID prefix.
- B
Use the order ID as the row key and store customer ID as a column.
Why wrong: This would require scanning all rows to find orders for a customer.
- C
Use a hash of the customer ID as the row key.
Why wrong: Hashing defeats the ability to scan all orders for a customer.
- D
Use a random UUID as the row key.
Why wrong: A random UUID does not group orders by customer.
Question 921 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.
An engineer is migrating a workload from a relational database to Bigtable. The current schema has a Customers table (1M rows) and an Orders table (100M rows) with a foreign key. Queries often fetch all orders for a customer. What is the best row key design for the Bigtable orders table?
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 customer ID + order ID as the row key (e.g., cust123#ord456).
Option A is correct because using customer ID + order ID as the row key ensures that all orders for a single customer are stored in contiguous rows, enabling efficient range scans. Bigtable orders rows lexicographically by row key, so a prefix scan on the customer ID retrieves all related orders in a single read operation, avoiding expensive joins or scatter-gather patterns.
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 customer ID + order ID as the row key (e.g., cust123#ord456).
Why this is correct
This enables efficient scans by customer ID prefix.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the order ID as the row key and store customer ID as a column.
Why it's wrong here
This would require scanning all rows to find orders for a customer.
- ✗
Use a hash of the customer ID as the row key.
Why it's wrong here
Hashing defeats the ability to scan all orders for a customer.
- ✗
Use a random UUID as the row key.
Why it's wrong here
A random UUID does not group orders by customer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a unique row key (like UUID or hash) is always best for distribution, ignoring that Bigtable's access pattern requires locality for range queries, which is the core trade-off in NoSQL row key design.
Detailed technical explanation
How to think about this question
Bigtable's row key design directly impacts performance because it uses a single-level sorted map (LSM-tree) where rows are stored in lexicographic order. A composite key like 'cust123#ord456' leverages Bigtable's ability to perform prefix scans (e.g., row key range 'cust123#' to 'cust123~') to read all orders for a customer in one sequential I/O pass, which is critical for latency-sensitive applications like real-time analytics or customer 360 views.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Use customer ID + order ID as the row key (e.g., cust123#ord456). — Option A is correct because using customer ID + order ID as the row key ensures that all orders for a single customer are stored in contiguous rows, enabling efficient range scans. Bigtable orders rows lexicographically by row key, so a prefix scan on the customer ID retrieves all related orders in a single read operation, avoiding expensive joins or scatter-gather patterns.
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.
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
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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