- A
Create a secondary index on Timestamp.
A secondary index on Timestamp allows efficient range scans.
- B
Create a covering index that includes all queried columns.
A covering index eliminates the need to access the base table, speeding up queries.
- C
Add a hash prefix to EventId to distribute writes.
Why wrong: This improves write distribution but does not help range queries on Timestamp.
- D
Use interleaving with a parent table on EventId.
Why wrong: Interleaving is for colocating parent-child rows, not for range queries on a non-key column.
- E
Change the primary key to (Timestamp, EventId).
Why wrong: While this could allow range scans, it may create hotspots and is a fundamental schema change with risks.
Question 747 of 1,000
PCDE Design and implement database schemas Practice Question
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.
A company uses Cloud Spanner with a schema that includes a table 'Events' with primary key (EventId, Timestamp). They need to run range queries on Timestamp across all events. They notice slow queries. Which two actions can improve query performance? (Choose two.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"primary"Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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
✓
Create a secondary index on Timestamp.
Option A is correct because creating a secondary index on Timestamp allows Cloud Spanner to efficiently perform range queries on that column without scanning the entire table. Without this index, Spanner must perform a full table scan, which is slow for large datasets. The secondary index provides a sorted structure that directly supports the range scan operation.
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 secondary index on Timestamp.
Why this is correct
A secondary index on Timestamp allows efficient range scans.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Create a covering index that includes all queried columns.
Why this is correct
A covering index eliminates the need to access the base table, speeding up queries.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Add a hash prefix to EventId to distribute writes.
Why it's wrong here
This improves write distribution but does not help range queries on Timestamp.
- ✗
Use interleaving with a parent table on EventId.
Why it's wrong here
Interleaving is for colocating parent-child rows, not for range queries on a non-key column.
- ✗
Change the primary key to (Timestamp, EventId).
Why it's wrong here
While this could allow range scans, it may create hotspots and is a fundamental schema change with risks.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google often tests the distinction between indexing strategies that improve write distribution (like hash prefixes) versus those that improve read performance for range scans, and candidates mistakenly choose hash prefixes for range queries.
Detailed technical explanation
How to think about this question
Cloud Spanner uses a distributed storage system where secondary indexes are stored as separate tables with their own split points. A covering index (Option B) includes all columns queried, so Spanner can satisfy the query entirely from the index without fetching rows from the base table, reducing read latency and CPU usage. In practice, for range queries on Timestamp, a secondary index on Timestamp alone may still require a back-join to retrieve other columns, so a covering index that includes all queried columns is often the optimal choice.
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 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: Create a secondary index on Timestamp. — Option A is correct because creating a secondary index on Timestamp allows Cloud Spanner to efficiently perform range queries on that column without scanning the entire table. Without this index, Spanner must perform a full table scan, which is slow for large datasets. The secondary index provides a sorted structure that directly supports the range scan operation.
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.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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