- A
Create a separate column family for each event type.
Why wrong: Column families are logical groupings and do not directly improve filtering performance.
- B
Add a secondary index on the event_type column.
Why wrong: Cloud Bigtable does not support secondary indexes; row key design is the primary access pattern.
- C
Use a separate Bigtable instance for each event type.
Why wrong: This is an overly complex and expensive solution, not a schema design change.
- D
Change the row key to 'event_type#customer_id#timestamp'.
This allows efficient range scans for a specific event type across all customers.
Question 714 of 1,000
Bigtable Row Key Design: Event Type First for Filtering
This PCDE practice question tests your understanding of design and implement database schemas. 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 e-commerce platform uses Cloud Bigtable for real-time analytics on customer behavior. The table uses a row key of 'customer_id#timestamp' (customer ID followed by reverse timestamp). Queries for a specific customer's recent events are fast, but queries that filter by event type (e.g., 'purchase') across many customers are slow. What schema change can improve query performance for event-type filtering?
Quick Answer
The answer is to change the row key to 'event_type#customer_id#timestamp'. This is correct because Cloud Bigtable stores rows in lexicographic order by row key, so placing the event type first allows a scan to target a contiguous range of rows for a specific event type, dramatically improving filter performance. On the Google Professional Cloud Database Engineer exam, this tests your understanding that Bigtable’s single-index design forces you to model query patterns into the row key itself—a common trap is assuming secondary indexes or column families can substitute for key design. Remember the memory tip: “First in the key, first in the scan”—the leftmost part of the row key determines the primary access pattern, so always lead with your most frequent filter criterion.
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
✓
Change the row key to 'event_type#customer_id#timestamp'.
Option D is correct because Cloud Bigtable's performance depends heavily on row key design for efficient scans. By changing the row key to 'event_type#customer_id#timestamp', queries filtering by event type can use a single row key prefix scan, which is fast and avoids full table scans. This leverages Bigtable's lexicographic ordering to group all events of the same type together, making event-type filtering a range scan rather than a filter across unrelated rows.
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.
- ✗
Create a separate column family for each event type.
Why it's wrong here
Column families are logical groupings and do not directly improve filtering performance.
- ✗
Add a secondary index on the event_type column.
Why it's wrong here
Cloud Bigtable does not support secondary indexes; row key design is the primary access pattern.
- ✗
Use a separate Bigtable instance for each event type.
Why it's wrong here
This is an overly complex and expensive solution, not a schema design change.
- ✓
Change the row key to 'event_type#customer_id#timestamp'.
Why this is correct
This allows efficient range scans for a specific event type across all customers.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many candidates mistakenly think Bigtable supports secondary indexes like a relational database, leading them to choose Option B. However, Bigtable's architecture requires all access patterns to be designed into the row key for optimal performance.
Detailed technical explanation
How to think about this question
Bigtable stores rows sorted by row key in lexicographic order, so a row key prefix scan is the most efficient way to retrieve a subset of data. By placing 'event_type' first in the row key, all rows with the same event type become contiguous, allowing a single scan with a start and end key. This design pattern is critical for time-series or event data where filtering by a high-cardinality attribute is common, and it avoids the anti-pattern of using a customer-centric key that scatters events across the table.
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
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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: Change the row key to 'event_type#customer_id#timestamp'. — Option D is correct because Cloud Bigtable's performance depends heavily on row key design for efficient scans. By changing the row key to 'event_type#customer_id#timestamp', queries filtering by event type can use a single row key prefix scan, which is fast and avoids full table scans. This leverages Bigtable's lexicographic ordering to group all events of the same type together, making event-type filtering a range scan rather than a filter across unrelated rows.
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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