PCDE Plan and manage database infrastructure Practice Question
A company is migrating an on-premises Oracle database to Cloud SQL for PostgreSQL. The database is 2 TB in size and the network bandwidth to Google Cloud is limited to 500 Mbps. The migration window is 48 hours. Which migration strategy should the Database Engineer recommend?
⚠ Common exam trap
Test-takers frequently assume Database Migration Service (Option B) is always the best choice for any migration, but they overlook that continuous replication is unnecessary for a one-time migration and that the initial load still faces the same bandwidth bottleneck as other network-based methods.
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
✓
Export the database to flat files, compress, upload to Cloud Storage, then import to Cloud SQL.
The 2 TB database size and 500 Mbps bandwidth yield a theoretical transfer time of approximately 9.5 hours (2 TB * 1024 GB/TB * 8 bits/byte / 500 Mbps / 3600 seconds/hour), which fits within the 48-hour window. However, pg_dump/pg_restore over a VPN (Option A) would be slower due to TCP overhead and latency, and Database Migration Service with continuous replication (Option B) requires ongoing connectivity and may not complete the initial load within the window. Exporting to flat files, compressing them (e.g., with gzip), uploading to Cloud Storage, and then importing to Cloud SQL leverages high-throughput parallel uploads and avoids network latency issues, making it the most reliable strategy for a one-time migration within the given constraints.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a VPN tunnel and use pg_dump/pg_restore over the network.
Why it's wrong here
pg_dump over VPN is slower and less reliable than file-based migration.
- ✗
Use Database Migration Service with continuous replication.
Why it's wrong here
Continuous replication requires higher bandwidth and may not complete within 48 hours.
- ✓
Export the database to flat files, compress, upload to Cloud Storage, then import to Cloud SQL.
Why this is correct
File-based migration with compression can work within the bandwidth and time constraints.
- ✗
Request a dedicated interconnect and then migrate.
Why it's wrong here
Setting up interconnect takes weeks, exceeding the migration window.
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