PCDE Practice Question: Deploy scalable and highly available databases in Google Cloud
A company uses Cloud Spanner multi-region with the nam-eur-asia1 configuration. They experience a regional outage that affects two of the three regions. What is the expected behavior regarding read and write availability?
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
✓
Read and write availability are unaffected because Spanner automatically fails over to remaining regions.
Spanner multi-region with 5+ regions (like nam-eur-asia1 which has 3 regions with multiple zones each) can tolerate the loss of up to two regions while maintaining read/write availability. The remaining region(s) will continue to serve reads and writes. However, if the leader region is lost, a new leader is elected from remaining regions, which may cause a brief write unavailability (RTO <1 min). Spanner guarantees 99.999% availability for multi-region instances.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Reads are available but writes are unavailable until the leader region recovers.
Why it's wrong here
Spanner can elect a new leader from remaining regions, so writes can continue after leader re-election (typically <1 min).
- ✗
The entire instance becomes unavailable due to loss of quorum.
Why it's wrong here
With nam-eur-asia1, the instance has 3 regions, each with multiple zones. Even with two regions down, the third region can maintain quorum for writes. The instance remains available.
- ✗
The instance becomes read-only until at least two regions recover.
Why it's wrong here
Spanner requires a majority of replicas for writes, but with 3 regions and multiple zones, a majority can be formed from remaining regions. Writes are possible.
- ✓
Read and write availability are unaffected because Spanner automatically fails over to remaining regions.
Why this is correct
Spanner multi-region with nam-eur-asia1 (3 regions, multiple zones each) can tolerate loss of two regions. The remaining region(s) continue to serve reads and writes, with a brief failover if leader region is lost.
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Same concept, more angles
2 more ways this is tested on PCDE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A financial services firm runs a multi-region Spanner instance with the nam-eur-asia1 configuration. They need to ensure that if the leader region (us-central1) becomes unavailable, failover to another region occurs automatically within 1 minute. What is the expected RPO and RTO for this scenario?
hard- ✓ A.RPO ~ 15 seconds, RTO < 1 minute
- B.RPO ~ 0, RTO ~ 15 seconds
- C.RPO ~ 1 hour, RTO ~ 5 minutes
- D.RPO = 0, RTO < 1 minute
Why A: Spanner multi-region configurations provide automatic failover with RTO under 1 minute. For the nam-eur-asia1 configuration, it is a multi-region with multiple read-write replicas. The RPO is approximately 15 seconds because Spanner uses quorum-based replication; in the event of a region failure, a small number of recent transactions may be uncommitted.
Variation 2. A financial services company runs a global trading application on Cloud Spanner. They need the highest availability with 99.999% SLA and automatic failover with zero data loss. Which Spanner configuration should they choose?
medium- ✓ A.Multi-region configuration nam-eur-asia1 (US, Europe, Asia)
- B.Regional configuration in us-central1 with read replicas
- C.Multi-region configuration nam6 (US, limited to North America)
- D.Regional configuration with a cross-region standby using backup/restore
Why A: Multi-region configurations provide 99.999% SLA. Among the options, nam-eur-asia1 spans three continents with read-write replicas in each continent, offering automatic failover with zero data loss (RPO=0). Regional configuration offers 99.99% SLA. Multi-region with only read-only replicas in some regions does not achieve the same failover capability.
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.