The answer is to enable AOF (Append-Only File) persistence on the Cloud Memorystore for Redis instance. This is correct because AOF durability logs every write operation to disk, so when a failover occurs in a standard tier with replication, the promoted replica can replay the AOF file to recover recent writes that were still in memory, drastically reducing data loss beyond what asynchronous replication alone provides. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding that standard tier replication handles high availability but not crash consistency—persistence is a separate knob. A common trap is assuming replication alone guarantees data survival; it does not, as the replica may lag behind the primary. Memory tip: think “AOF = All Operations File” for failover recovery, while RDB snapshots are better for bulk backup but risk losing more recent data.
PCDE Plan and manage database infrastructure Practice Question
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.
A company uses Cloud Memorystore for Redis as a cache for their web application. They want to ensure that cache data survives a failover event with minimal data loss. The current instance has a standard tier (with replication) and persistence disabled. What change should they make?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable persistence (AOF) on the instance.
Enabling AOF (Append-Only File) persistence on a Cloud Memorystore for Redis standard tier instance ensures that write operations are durably logged to disk. In the event of a failover, the promoted replica can replay the AOF to recover the most recent writes, minimizing data loss beyond what the default in-memory replication provides.
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.
✗
Switch to the basic tier without replication but with high memory.
Why it's wrong here
Basic tier has no replication or persistence; data loss on failure is higher.
✓
Enable persistence (AOF) on the instance.
Why this is correct
Persistence ensures data is written to disk and can be recovered after failover.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the instance memory size to hold more data.
Why it's wrong here
Does not prevent data loss on failover.
✗
Add a read replica to the instance.
Why it's wrong here
Read replicas do not provide automatic failover or persistence; they are for read scaling.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume replication alone guarantees data durability, but replication only copies data in memory and does not protect against loss of uncommitted writes during a failover without disk-based persistence enabled.
Detailed technical explanation
How to think about this question
AOF persistence works by appending every write operation to a log file, which can be replayed on restart or failover to restore state. Cloud Memorystore for Redis supports both AOF and RDB persistence; AOF provides finer-grained durability (typically every second or per write, depending on fsync policy) compared to RDB snapshots. In a standard tier failover, the new primary replays its AOF to recover writes that were acknowledged but not yet replicated to the old replica, reducing the window of data loss to near zero if configured with 'always' fsync.
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: Enable persistence (AOF) on the instance. — Enabling AOF (Append-Only File) persistence on a Cloud Memorystore for Redis standard tier instance ensures that write operations are durably logged to disk. In the event of a failover, the promoted replica can replay the AOF to recover the most recent writes, minimizing data loss beyond what the default in-memory replication provides.
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.
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Question Discussion
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