Question 32 of 1,446
PostgreSQL to Cloud SQL Migration: Minimal Downtime with DMS
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?
Quick Answer
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.
⚠ Common exam trap
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.
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
✓
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.
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.
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Same concept, more angles
1 more way 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 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.
Last reviewed: Jun 30, 2026
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