- A
Use two-phase commit (2PC) across both databases.
Why wrong: 2PC is not supported across Cloud SQL and Bigtable; also it adds latency and complexity.
- B
Implement a saga pattern with compensating transactions in case of failure.
Saga pattern coordinates distributed transactions with rollback steps.
- C
Design for strong consistency by using global transactions.
Why wrong: Strong consistency across different database types is very hard to achieve and not recommended for cross-database solutions.
- D
Use idempotent receivers and retry logic to handle duplicate events.
Idempotency and retries are key for eventual consistency.
- E
Write directly to both databases in a single synchronous call.
Why wrong: This couples the systems and can cause failures; it does not handle consistency.
PCD Practice Question: Manage a Solution that Can Span Multiple Database Systems
This PCD practice question tests your understanding of manage a solution that can span multiple database systems. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is designing a cross-database solution with eventual consistency. They need to update data in Cloud SQL (orders) and Bigtable (inventory) as part of a single business transaction. Which two patterns can help maintain eventual consistency? (Choose two.)
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 in case of failure.
Option B is correct because the saga pattern breaks a distributed transaction into a series of local transactions, each with a compensating action that can undo its effects if a subsequent step fails. This pattern is ideal for maintaining eventual consistency across Cloud SQL and Bigtable without requiring a global coordinator or locking resources. Option D is correct because idempotent receivers ensure that duplicate events (e.g., from retries or network failures) do not cause unintended side effects, and retry logic allows the system to recover from transient failures, both of which are essential for achieving eventual consistency in a cross-database solution.
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.
- ✗
Use two-phase commit (2PC) across both databases.
Why it's wrong here
2PC is not supported across Cloud SQL and Bigtable; also it adds latency and complexity.
- ✓
Implement a saga pattern with compensating transactions in case of failure.
Why this is correct
Saga pattern coordinates distributed transactions with rollback steps.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Design for strong consistency by using global transactions.
Why it's wrong here
Strong consistency across different database types is very hard to achieve and not recommended for cross-database solutions.
- ✓
Use idempotent receivers and retry logic to handle duplicate events.
Why this is correct
Idempotency and retries are key for eventual consistency.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Write directly to both databases in a single synchronous call.
Why it's wrong here
This couples the systems and can cause failures; it does not handle consistency.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between strong consistency patterns (like 2PC and global transactions) and eventual consistency patterns (like sagas and idempotent retries), trapping candidates who assume that any transaction pattern can be adapted to eventual consistency without understanding the fundamental trade-offs.
Detailed technical explanation
How to think about this question
The saga pattern can be implemented using choreography (each service publishes events that trigger the next step) or orchestration (a central coordinator manages the sequence). In a real-world scenario, if an order is inserted into Cloud SQL but the inventory update in Bigtable fails, a compensating transaction (e.g., deleting the order or marking it as failed) is executed to revert the state. Idempotency is often achieved by including a unique idempotency key in each event, allowing the receiver to detect and discard duplicates, which is critical when using retry logic with exponential backoff.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCD question test?
Manage a Solution that Can Span Multiple Database Systems — This question tests Manage a Solution that Can Span Multiple Database Systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement a saga pattern with compensating transactions in case of failure. — Option B is correct because the saga pattern breaks a distributed transaction into a series of local transactions, each with a compensating action that can undo its effects if a subsequent step fails. This pattern is ideal for maintaining eventual consistency across Cloud SQL and Bigtable without requiring a global coordinator or locking resources. Option D is correct because idempotent receivers ensure that duplicate events (e.g., from retries or network failures) do not cause unintended side effects, and retry logic allows the system to recover from transient failures, both of which are essential for achieving eventual consistency in a cross-database solution.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jul 4, 2026
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.
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