- A
Shadow writes (dual-write to both databases)
Sends writes to both old and new DB for comparison.
- B
Rollback plan documentation
Why wrong: Important for planning, not a testing technique.
- C
Load testing with production data shape
Why wrong: Useful for performance testing, but not specifically for data correctness.
- D
Database Migration Service continuous migration
Why wrong: This is a migration method, not a testing technique.
- E
Comparison queries to validate data consistency
Queries that compare data between old and new DB.
Question 129 of 999
PCD Migrate Data Solutions Practice Question
This PCD practice question tests your understanding of migrate data solutions. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 migrating a MySQL database to Cloud SQL. They want to test the migration by sending writes to both the old and new databases simultaneously and comparing results. Which TWO techniques 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
✓
Shadow writes (dual-write to both databases)
Shadow writes, also known as dual-writes, allow the application to send the same write operations to both the old MySQL database and the new Cloud SQL database simultaneously. This technique enables real-time comparison of the results from both databases to verify that the migration is handling writes correctly without disrupting the existing production workload.
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.
- ✓
Shadow writes (dual-write to both databases)
Why this is correct
Sends writes to both old and new DB for comparison.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Rollback plan documentation
Why it's wrong here
Important for planning, not a testing technique.
- ✗
Load testing with production data shape
Why it's wrong here
Useful for performance testing, but not specifically for data correctness.
- ✗
Database Migration Service continuous migration
Why it's wrong here
This is a migration method, not a testing technique.
- ✓
Comparison queries to validate data consistency
Why this is correct
Queries that compare data between old and new DB.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between techniques that validate data consistency (shadow writes + comparison queries) versus tools that handle replication or performance testing, leading candidates to mistakenly select load testing or continuous migration as methods for write verification.
Detailed technical explanation
How to think about this question
Shadow writes typically require the application to be modified to write to both databases within the same transaction or asynchronously, often using a write-ahead log or a queue to ensure consistency. In a real-world scenario, you might use a tool like ProxySQL or a custom middleware to intercept writes and duplicate them, then run periodic comparison queries (e.g., using checksums or row-by-row verification) to detect discrepancies. This approach is especially useful for validating schema changes or data transformation logic before cutting over to Cloud SQL.
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.
- →
Migrate Data Solutions — study guide chapter
Learn the concepts, then practise the questions
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Migrate Data Solutions practice questions
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FAQ
Questions learners often ask
What does this PCD question test?
Migrate Data Solutions — This question tests Migrate Data Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Shadow writes (dual-write to both databases) — Shadow writes, also known as dual-writes, allow the application to send the same write operations to both the old MySQL database and the new Cloud SQL database simultaneously. This technique enables real-time comparison of the results from both databases to verify that the migration is handling writes correctly without disrupting the existing production workload.
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
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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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