- A
Secondary indexes maintain strong consistency with the base table
All indexes in Spanner are strongly consistent.
- B
Secondary indexes are automatically used for queries that filter on primary key columns
Why wrong: Primary key queries use the primary index; secondary indexes are not automatically used for PK filters.
- C
Secondary indexes require a unique constraint
Why wrong: Secondary indexes can be non-unique; unique constraint is optional.
- D
Secondary indexes can be created on child tables without including the parent key
They are still valid secondary indexes, though not interleaved.
- E
Secondary indexes can be created with a STORING clause to include non-key columns
Correct; STORING clause stores additional columns in the index for covering queries.
Question 994 of 1,000
Cloud Spanner Secondary Index — Design Considerations and Best Practices
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.
Which three of the following are valid considerations when designing secondary indexes in Cloud Spanner? (Choose three.)
Quick Answer
The answer is that secondary indexes can be created with a STORING clause to include non-key columns, they are strongly consistent with the base table, and they can be created on child tables without including the parent key. These three considerations are valid because Cloud Spanner secondary indexes are designed to provide global, strongly consistent lookups without requiring the parent key from an interleaved hierarchy, and the STORING clause allows you to embed additional columns to avoid a back-join to the base table. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of how secondary indexes differ from primary and interleaved indexes, with a common trap being the assumption that secondary indexes are automatically used for primary key filtering or that they must be unique. A useful memory tip is "STORING stores, not unique" — remember that STORING adds non-key columns for covering queries, and uniqueness is optional, not required.
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
✓
Secondary indexes maintain strong consistency with the base table
Option A is correct because Cloud Spanner secondary indexes are fully synchronous with the base table, meaning they are updated atomically in the same transaction as the table write. This ensures that reads using the secondary index always return strongly consistent data, without any eventual consistency window.
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.
- ✓
Secondary indexes maintain strong consistency with the base table
Why this is correct
All indexes in Spanner are strongly consistent.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Secondary indexes are automatically used for queries that filter on primary key columns
Why it's wrong here
Primary key queries use the primary index; secondary indexes are not automatically used for PK filters.
- ✗
Secondary indexes require a unique constraint
Why it's wrong here
Secondary indexes can be non-unique; unique constraint is optional.
- ✓
Secondary indexes can be created on child tables without including the parent key
Why this is correct
They are still valid secondary indexes, though not interleaved.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Secondary indexes can be created with a STORING clause to include non-key columns
Why this is correct
Correct; STORING clause stores additional columns in the index for covering queries.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common misconception is that secondary indexes in Cloud Spanner are automatically used for any query filter. In reality, the optimizer only uses a secondary index when the query filter columns match the index key. Filters on primary key columns will not automatically leverage secondary indexes; they use the primary index instead.
Detailed technical explanation
How to think about this question
Under the hood, Cloud Spanner implements secondary indexes as separate tables that are interleaved with the base table's primary key, ensuring atomic updates via the same Paxos-based distributed transaction protocol. The STORING clause (option E) allows you to include non-key columns in the index to avoid an extra lookup back to the base table, which is critical for reducing read latency in high-throughput applications.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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: Secondary indexes maintain strong consistency with the base table — Option A is correct because Cloud Spanner secondary indexes are fully synchronous with the base table, meaning they are updated atomically in the same transaction as the table write. This ensures that reads using the secondary index always return strongly consistent data, without any eventual consistency window.
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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