The answer is Database Migration Service with continuous replication. This is the correct choice because DMS uses change data capture (CDC) to replicate ongoing writes from the source PostgreSQL database to Cloud SQL while the initial 2 TB full load completes, enabling a cutover with only seconds of downtime even under a high write workload. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of migration strategies for large, active databases—the key trap is choosing a batch export/import method like pg_dump, which would cause hours of downtime and cannot handle continuous writes. Remember the memory tip: "CDC for CDC" — Continuous Data Capture for Continuous Database Changes.
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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 an on-premises PostgreSQL database to Cloud SQL. The database is 2 TB and has a high write workload. They need minimal downtime. Which migration approach is best?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Database Migration Service with continuous replication
Database Migration Service (DMS) with continuous replication is the best approach because it supports minimal-downtime migrations from on-premises PostgreSQL to Cloud SQL. DMS uses change data capture (CDC) to replicate ongoing writes while the initial data load completes, then performs a cutover with only seconds of downtime. This handles the 2 TB size and high write workload without requiring manual export/import or schema changes.
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 Cloud Spanner
Why it's wrong here
Cloud Spanner is a different database type; migration would require significant application changes.
✗
Use Cloud SQL for MySQL instead
Why it's wrong here
MySQL is not compatible with PostgreSQL schema and queries.
✗
Export using pg_dump and import via psql
Why it's wrong here
Export/import requires application downtime and is slow for 2 TB.
✓
Use Database Migration Service with continuous replication
Why this is correct
DMS with continuous replication minimizes downtime by keeping the target in sync.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that pg_dump/psql is suitable for large databases with high write workloads, but the trap here is that candidates overlook the need for minimal downtime and the fact that logical dumps require a consistent snapshot, which forces a read-only period or long-running transaction that blocks writes.
Detailed technical explanation
How to think about this question
Database Migration Service uses a replication slot on the source PostgreSQL to capture WAL (Write-Ahead Log) changes via the pgoutput logical replication plugin, enabling near-real-time CDC. During the initial backfill, DMS copies the full 2 TB dataset using parallel workers and streaming, then continuously applies incremental changes until cutover. The cutover involves stopping writes to the source, applying any remaining lag, and promoting the Cloud SQL instance as the new primary, typically achieving sub-minute downtime.
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.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use Database Migration Service with continuous replication — Database Migration Service (DMS) with continuous replication is the best approach because it supports minimal-downtime migrations from on-premises PostgreSQL to Cloud SQL. DMS uses change data capture (CDC) to replicate ongoing writes while the initial data load completes, then performs a cutover with only seconds of downtime. This handles the 2 TB size and high write workload without requiring manual export/import or schema changes.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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Variation 1. A company plans to migrate an on-premises PostgreSQL database to Cloud SQL. The database is 2 TB in size and requires minimal downtime. Which migration approach should they use?
easy
A.Export the database using pg_dump and import into Cloud SQL using psql.
B.Use Datastream to stream data into Cloud SQL.
✓ C.Use Database Migration Service with a continuous migration job.
D.Copy the data files to Cloud Storage and use gcloud to load into Bigtable.
Why C: Database Migration Service (DMS) with a continuous migration job is the correct approach because it supports minimal-downtime migrations from on-premises PostgreSQL to Cloud SQL. DMS uses logical replication (via PostgreSQL's pgoutput plugin) to continuously sync changes from the source to the target, allowing a short cutover window. For a 2 TB database, this avoids the lengthy downtime required by a full dump-and-load method.
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Question Discussion
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