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PCD Designing a polyglot persistence architecture Practice Question
A company is designing a polyglot persistence architecture. They need to use Cloud SQL for transactions, Bigtable for real-time analytics, and BigQuery for reporting. They also need to keep data across these systems eventually consistent. Which TWO approaches should they use?
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
✓
Implement a saga pattern with compensating transactions for each write.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Implement a saga pattern with compensating transactions for each write.
Why this is correct
Saga pattern is a standard approach for eventual consistency across polyglot stores.
- ✗
Use two-phase commit across all databases.
Why it's wrong here
Two-phase commit is not feasible across heterogeneous databases and would introduce tight coupling and latency.
- ✗
Use Cloud Spanner as a single database to avoid polyglot complexity.
Why it's wrong here
The scenario explicitly requires polyglot persistence, so using a single database is not the goal.
- ✗
Write to all three databases in a single transaction using distributed transactions.
Why it's wrong here
Distributed transactions across different database types are not supported and cause performance issues.
- ✓
Write to Cloud SQL and use Datastream to replicate changes to Bigtable and BigQuery.
Why this is correct
Datastream can capture CDC from Cloud SQL and stream to BigQuery (via GCS) and Bigtable (via Dataflow), ensuring eventual consistency.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCD 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 PCD exam.