The answer is long-running queries on the replica. When a read replica has a heavy query executing, it consumes system resources and blocks the background apply process from replaying WAL logs from the primary, directly causing replication lag. This happens because PostgreSQL on Cloud SQL applies changes sequentially on the replica, and any blocking operation stalls the entire pipeline. On the Google Professional Cloud Security Engineer exam, this concept tests your understanding of how replica performance, not just network or primary load, impacts data freshness. A common trap is assuming lag always stems from primary-side issues like high write volume, but the question explicitly states network and instance metrics are fine, steering you toward replica-side bottlenecks. Memory tip: think of the replica as a single-lane road—one slow truck (a long-running query) blocks all traffic behind it, creating a traffic jam of unapplied changes.
PCSE Practice Question: Managing operations in a cloud solution environment
This PCSE practice question tests your understanding of managing operations in a cloud solution environment. 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 Cloud SQL PostgreSQL instance is experiencing high replication lag between primary and read replica. You have verified the network and instance metrics. What is a likely cause?
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.
Automated backups can cause temporary performance impact but not sustained lag.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which PCSE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Managing operations in a cloud solution environment — This question tests Managing operations in a cloud solution environment — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Long-running queries on the replica — Long-running queries on the replica can block the apply process, increasing lag. Other options do not directly affect replication lag.
What should I do if I get this PCSE question wrong?
Identify which PCSE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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Question Discussion
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