Quick Answer
The answer is to increase the machine type of the replica. This directly reduces Cloud SQL read replica lag by providing more CPU and memory to apply binary log (binlog) events from the primary faster, since Cloud SQL for MySQL uses asynchronous replication where an underpowered replica cannot keep pace with the primary’s write throughput. On the Google Professional Cloud DevOps Engineer exam, this scenario tests your understanding that replication lag is a resource bottleneck on the replica side, not the primary—a common trap is to scale the primary or adjust timeouts, but the fix is always to give the replica more horsepower. Remember the mnemonic: “Lag is on the laggard”—the replica is the weak link, so beef it up, not the source.
This PCDOE practice question tests your understanding of optimizing service performance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 application uses Cloud SQL for MySQL and you notice that read replica lag is increasing. Which action would most likely reduce replica lag?
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.
Configure automatic failover to the replica.
Why wrong: Failover does not reduce lag.
Decrease the memory of the primary instance.
Why wrong: Less memory would slow down primary.
Increase the machine type of the replica.
More powerful replica can keep up with replication.
Promote the replica to a standalone instance.
Why wrong: Promotion does not reduce lag; it stops replication.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Increase the machine type of the replica.
Increasing the machine type of the replica (Option C) directly addresses read replica lag by providing more CPU and memory resources to the replica instance. This allows the replica to apply binary log (binlog) events from the primary faster, reducing the replication lag. Cloud SQL for MySQL uses asynchronous replication, so a replica with insufficient resources cannot keep up with the write throughput of the primary.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Configure automatic failover to the replica.
Why it's wrong here
Failover does not reduce lag.
Decrease the memory of the primary instance.
Why it's wrong here
Less memory would slow down primary.
Increase the machine type of the replica.
Why this is correct
More powerful replica can keep up with replication.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Promote the replica to a standalone instance.
Why it's wrong here
Promotion does not reduce lag; it stops replication.
Common exam traps
Google Cloud often tests the misconception that promoting a replica or failing over will resolve lag, but the correct approach is to scale the replica's resources to match the primary's write rate.
Detailed technical explanation
Cloud SQL for MySQL replication lag is measured in seconds and is influenced by the replica's ability to apply binlog events. Under the hood, the replica runs two threads: the I/O thread (fetching binlog from primary) and the SQL thread (applying events). Increasing the replica's machine type boosts both thread performance, especially the SQL thread, which is often the bottleneck. In real-world scenarios, a replica with 2 vCPU and 7.5 GB RAM may lag behind a primary with 8 vCPU and 32 GB RAM during peak write loads; upgrading the replica to match or exceed the primary's tier is a common mitigation.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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
Optimizing service performance — This question tests Optimizing service performance — Read the scenario before looking for a memorised answer..
The correct answer is: Increase the machine type of the replica. — Increasing the machine type of the replica (Option C) directly addresses read replica lag by providing more CPU and memory resources to the replica instance. This allows the replica to apply binary log (binlog) events from the primary faster, reducing the replication lag. Cloud SQL for MySQL uses asynchronous replication, so a replica with insufficient resources cannot keep up with the write throughput of the primary.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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