The answer is asynchronous replication to the failover replica. While Cloud SQL defaults to synchronous replication for failover replicas—which guarantees that every write is committed on both the primary and the replica before the transaction is acknowledged—configuring asynchronous replication introduces a lag window. During a failover event, any transactions that were committed on the primary but not yet replicated to the standby are permanently lost, making this the most likely cause of data loss. On the Google Professional Cloud Developer exam, this question tests your understanding of Cloud SQL replication modes and their impact on data durability; a common trap is assuming all replicas are synchronous by default. Remember the memory tip: “Sync is safe, async is fast—but failover with async means data loss that lasts.”
PCD Practice Question: Designing highly scalable, available, and reliable cloud-native applications
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native applications. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 running a high-traffic e-commerce platform on Google Cloud experiences occasional data loss in their Cloud SQL database during failover events. The database is configured with a failover replica in a different zone. What is the most likely cause of the data loss?
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
✓
The database is using asynchronous replication to the failover replica.
Cloud SQL uses synchronous replication for failover replicas by default, ensuring that transactions are committed on both the primary and the replica before acknowledging the write. If asynchronous replication is configured, the replica may lag behind the primary, and during a failover, any transactions not yet replicated are lost. This is the most likely cause of data loss during failover events.
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.
✗
Automated backups are not enabled.
Why it's wrong here
Backups are separate from failover replication.
✓
The database is using asynchronous replication to the failover replica.
Why this is correct
Asynchronous replication may not have replicated the most recent transactions before failover.
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 failover replica is configured as a read replica instead of a failover replica.
Why it's wrong here
Read replicas cannot be promoted during failover.
✗
The database is not using regional persistent disks.
Why it's wrong here
Regional persistent disks provide durability but not synchronous replication between zones.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between synchronous and asynchronous replication in the context of failover replicas, where candidates mistakenly assume all replicas are synchronous by default or confuse failover replicas with read replicas.
Detailed technical explanation
How to think about this question
Cloud SQL for MySQL and PostgreSQL uses semi-synchronous replication by default for failover replicas, which ensures at least one replica acknowledges the write before the primary commits. If asynchronous replication is used (e.g., by setting `rpl_semi_sync_master_enabled=OFF`), the replica can lag by hundreds of milliseconds or more, and during a sudden failover, unacknowledged transactions in the primary's binlog are lost. In high-traffic e-commerce platforms, write-heavy workloads exacerbate this lag, making data loss more likely during zone-level failures.
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.
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The database is using asynchronous replication to the failover replica. — Cloud SQL uses synchronous replication for failover replicas by default, ensuring that transactions are committed on both the primary and the replica before acknowledging the write. If asynchronous replication is configured, the replica may lag behind the primary, and during a failover, any transactions not yet replicated are lost. This is the most likely cause of data loss during failover events.
What should I do if I get this PCD 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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