PCDE Practice Question: Deploy scalable and highly available databases in Google Cloud
A social media company uses Cloud Spanner with a multi-region configuration. During a regional outage, automatic failover occurred, but some transactions that were in-flight at the time of failure were lost. What is the most likely reason for this data loss?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The multi-region configuration included read-only replicas in some regions, causing loss of recent writes
In a multi-region Spanner configuration, the leader region handles writes. If a transaction was committed but not yet replicated to other regions before the leader region failed, it could be lost if the new leader region does not have that data. However, Spanner's multi-region configurations are designed for RPO=0 (no data loss) when using read-write replicas. If read-only replicas are used in some regions, data loss can occur because those replicas do not participate in the voting. The most common cause of data loss in Spanner multi-region is a misconfiguration where not all regions have read-write replicas.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The database had schema changes that were not replicated to standby replicas
Why it's wrong here
Schema changes are applied consistently across all replicas in Spanner.
- ✗
The transaction isolation level was set to read committed instead of serializable
Why it's wrong here
Isolation level affects concurrency but not durability across failover.
- ✗
The application did not retry failed transactions after the failover
Why it's wrong here
Retry logic is important but does not cause data loss; it affects whether the application recovers successfully.
- ✓
The multi-region configuration included read-only replicas in some regions, causing loss of recent writes
Why this is correct
Only read-write replicas can become the new leader. If a region has only read-only replicas, committed transactions from the old leader may not be fully replicated before failover, resulting in data loss.
Go deeper
Related to this question
About these practice questions
Courseiva writes every PCDE question from scratch — 1,446 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDE exam.