The answer is using stale reads with a timestamp bound to allow reads from replicas. This is correct because stale reads enable Cloud Spanner to serve point lookups from read-only replicas, offloading CPU-intensive processing from the leading replica nodes. When high read throughput causes high CPU utilization on Spanner nodes, stale reads reduce read latency by distributing the workload across replicas that can serve slightly outdated data without contention. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of Spanner’s replication architecture and the trade-off between consistency and performance—a common trap is choosing to increase node capacity, which adds cost but doesn’t address the root cause of read-heavy CPU pressure. Remember the key insight: for point lookups that can tolerate staleness, offloading reads to replicas directly lowers CPU load and latency. Memory tip: “Stale saves CPU—fresh is for the lead.”
PCDE Monitor and optimize database performance Practice Question
This PCDE practice question tests your understanding of monitor and optimize database performance. 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.
Your Spanner instance is running a workload with high read throughput. You notice that read latency has increased significantly. Upon investigating, you find that the instance is experiencing high CPU utilization on the Spanner nodes. The workload consists of many small point lookups (reads by primary key). Which action is most likely to reduce read latency?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use stale reads with a timestamp bound to allow reads from replicas.
B is correct because stale reads allow Cloud Spanner to serve read requests from read-only replicas, which offloads CPU-intensive processing from the leading replica nodes. By using a timestamp bound (e.g., exact_staleness or max_staleness), the workload can tolerate slightly outdated data, reducing the load on the nodes and lowering read latency for point lookups.
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.
✗
Add secondary indexes on the primary key columns.
Why it's wrong here
Secondary indexes are redundant for point lookups by primary key.
✓
Use stale reads with a timestamp bound to allow reads from replicas.
Why this is correct
Stale reads can be served from any replica, reducing load on the leader and improving latency.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Redesign the schema to use interleaved tables.
Why it's wrong here
Interleaved tables optimize joins, not point lookups.
✗
Reduce the number of Spanner nodes to lower CPU overhead.
Why it's wrong here
Fewer nodes may increase load per node.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that reducing nodes or adding indexes always improves performance, but in Spanner, reducing nodes starves CPU capacity and secondary indexes increase write overhead, while stale reads directly offload the leader's CPU.
Detailed technical explanation
How to think about this question
Cloud Spanner uses a multi-version concurrency control (MVCC) system where stale reads can be served by any replica without contacting the leader, leveraging Paxos-based replication. The read timestamp bound (e.g., exact_staleness of 15 seconds) allows the system to bypass the leader's CPU for strong reads, distributing the load across read-only replicas. In real-world scenarios, this is critical for read-heavy workloads like real-time dashboards where eventual consistency is acceptable.
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.
Monitor and optimize database performance — This question tests Monitor and optimize database performance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use stale reads with a timestamp bound to allow reads from replicas. — B is correct because stale reads allow Cloud Spanner to serve read requests from read-only replicas, which offloads CPU-intensive processing from the leading replica nodes. By using a timestamp bound (e.g., exact_staleness or max_staleness), the workload can tolerate slightly outdated data, reducing the load on the nodes and lowering read latency for point lookups.
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: "most likely", "primary". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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