The answer is that transaction logs for point-in-time recovery are consuming disk space. This occurs because Cloud SQL for PostgreSQL uses Write-Ahead Log (WAL) files to enable PITR, and these logs accumulate on the instance’s disk until they are automatically purged after the configured backup retention window. When the rate of transaction log generation outpaces the cleanup process—often due to heavy write workloads or a long retention period—the logs fill the storage volume, causing the database to run out of space and potentially go offline. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of how PITR interacts with storage management; a common trap is assuming automated backups alone prevent disk issues, when in fact the logs themselves are the culprit. A useful memory tip: “WAL files wait for retention—if writes are wild, storage is stolen.”
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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.
A company notices that their Cloud SQL for PostgreSQL instance, as shown in the exhibit, frequently runs out of storage, causing downtime. They have set up automated backups with point-in-time recovery. What is the most likely cause of the storage issue?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Transaction logs for point-in-time recovery are consuming disk space.
The correct answer is A because Cloud SQL for PostgreSQL uses transaction logs (WAL files) to enable point-in-time recovery (PITR). These logs accumulate on the disk until they are automatically removed, but if the rate of log generation exceeds the cleanup rate or if the backup retention period is long, the logs can fill the disk, causing storage exhaustion and downtime.
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.
✓
Transaction logs for point-in-time recovery are consuming disk space.
Why this is correct
Transaction logs are stored on the same disk and can grow large.
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.
✗
The activation policy is set to ALWAYS, causing continuous writes.
Why it's wrong here
Activation policy does not affect storage usage.
✗
The instance tier (db-custom-4-15360) is too low for the workload.
Why it's wrong here
Tier affects CPU and memory, not storage.
✗
The data disk type (PD_SSD) is not suitable for PostgreSQL.
Why it's wrong here
PD_SSD is appropriate.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that storage issues are caused by instance tier or disk type, when in fact the hidden culprit is transaction log accumulation from point-in-time recovery settings.
Detailed technical explanation
How to think about this question
Cloud SQL for PostgreSQL stores WAL segments in the pg_wal directory; these are retained for the duration of the PITR backup retention window (default 7 days). If the database has a high write workload, WAL generation can outpace the automatic log cleanup, especially when the retention period is long or when the instance has insufficient storage headroom. A common real-world scenario is a bulk data load or a long-running transaction that generates many WAL files, causing the disk to fill before old logs are purged.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
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: Transaction logs for point-in-time recovery are consuming disk space. — The correct answer is A because Cloud SQL for PostgreSQL uses transaction logs (WAL files) to enable point-in-time recovery (PITR). These logs accumulate on the disk until they are automatically removed, but if the rate of log generation exceeds the cleanup rate or if the backup retention period is long, the logs can fill the disk, causing storage exhaustion and downtime.
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". 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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Question Discussion
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