- A
Use read-only replicas (follower reads)
Follower reads allow reads from nearby replicas instead of the leader, reducing latency.
- B
Use multi-region configuration
Multi-region places data closer to users across regions, reducing read latency.
- C
Use leader reads
Why wrong: Leader reads are not a standard feature; reads are always from the leader in a multi-region setup unless using follower reads.
- D
Use interleaved tables
Why wrong: Interleaved tables reduce join overhead but do not address global read latency.
- E
Use secondary indexes
Indexes allow efficient lookups without scanning the entire table, reducing latency.
Question 165 of 1,000
Reducing Cloud Spanner Read Latency — Follower Reads & Indexes | Google PCDE Explained
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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 actions can reduce read latency for a globally distributed Cloud Spanner database?
Quick Answer
The answer is to use secondary indexes, along with follower reads and read-only replicas, to reduce Cloud Spanner read latency. Secondary indexes allow queries to avoid full table scans by locating data directly, while follower reads offload read requests to nearby non-leader replicas, cutting down network distance and response time for globally distributed users. On the Google Professional Cloud Database Engineer exam, this concept tests your understanding of trade-offs between consistency and performance: follower reads sacrifice strong consistency for lower latency, making them ideal for use cases like dashboards or analytics. A common trap is assuming all reads must hit the leader replica, but the exam expects you to recognize that read-only replicas serve stale reads (up to a few seconds old) much faster. To remember this, think “follow the follower for speed, not the leader for consistency.”
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 read-only replicas (follower reads)
Option A is correct because read-only replicas (follower reads) allow Cloud Spanner to serve read requests from non-leader replicas, reducing the distance data must travel and thus lowering read latency for globally distributed users. This is particularly effective when strong consistency is not required, as follower reads can return data that is up to a few seconds stale but much faster to access from a nearby replica.
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 read-only replicas (follower reads)
Why this is correct
Follower reads allow reads from nearby replicas instead of the leader, reducing latency.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Use multi-region configuration
Why this is correct
Multi-region places data closer to users across regions, reducing read latency.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use leader reads
Why it's wrong here
Leader reads are not a standard feature; reads are always from the leader in a multi-region setup unless using follower reads.
- ✗
Use interleaved tables
Why it's wrong here
Interleaved tables reduce join overhead but do not address global read latency.
- ✓
Use secondary indexes
Why this is correct
Indexes allow efficient lookups without scanning the entire table, reducing latency.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that leader reads are always optimal for latency, but the trap here is that leader reads actually increase latency for distant users because they force all reads to the single leader region, while follower reads distribute read traffic to the nearest replica.
Detailed technical explanation
How to think about this question
Follower reads leverage Cloud Spanner's TrueTime API to serve reads from any replica that has sufficiently recent data, typically within 10 seconds of staleness. This allows read traffic to be load-balanced across all replicas in a multi-region configuration, reducing contention on the leader and enabling sub-10ms read latencies for users close to a non-leader replica. In practice, applications like global user profiles or product catalogs benefit greatly from follower reads by serving reads from the nearest replica while still maintaining eventual consistency.
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
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCDE question test?
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use read-only replicas (follower reads) — Option A is correct because read-only replicas (follower reads) allow Cloud Spanner to serve read requests from non-leader replicas, reducing the distance data must travel and thus lowering read latency for globally distributed users. This is particularly effective when strong consistency is not required, as follower reads can return data that is up to a few seconds stale but much faster to access from a nearby replica.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on PCDE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A database administrator notices that the Spanner instance has only 3 nodes, but the application experiences high read latency during peak hours. The team needs to improve performance without over-provisioning. What should they do?
hard- A.Increase node count to 6
- B.Use an interleaved table
- C.Enable point-in-time recovery
- D.Change to a multi-region configuration
- ✓ E.Create a secondary index
Why E: Option E is correct because creating a secondary index on frequently queried columns allows Spanner to avoid full table scans, reducing read latency without increasing nodes. Option A (increase node count) would provision more compute and storage capacity, but if CPU utilization is not high, it constitutes over-provisioning. Option B (interleaved table) improves performance for parent-child joins but does not help general read queries. Option C (enable point-in-time recovery) adds storage costs for versioned data without directly improving read latency. Option D (change to multi-region configuration) increases write latency and cost due to replication across regions, and may not reduce read latency in a single-region setup.
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Last reviewed: Jun 30, 2026
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