Migrating PostgreSQL Databases to Cloud SQL Seamlessly
Migrating PostgreSQL to Cloud SQL can be done with minimal downtime and high reliability if you follow the right method. Google Cloud supports multiple migration strategies—choosing the right one depends on your data size, downtime tolerance, and environment.
1. Pre-Migration Checklist
Before migration, ensure:
A. Cloud SQL PostgreSQL instance is created
Choose machine type (Shared/Core, Memory, Storage)
Set PostgreSQL version
Configure region, zone, network
Enable automatic backups & Point-in-Time Recovery (PITR)
Create users and databases that match source roles (optional but helpful)
B. Configure network connectivity
For on-prem or other clouds:
Use Cloud VPN, Cloud Interconnect, or Cloud SQL Auth Proxy
For another GCP service:
Use private IP for best security and latency
C. Check compatibility
Run:
SELECT version();
and ensure extensions used on source PostgreSQL are supported by Cloud SQL.
2. Migration Approaches
There are three main methods to migrate PostgreSQL into Cloud SQL.
Method 1: pg_dump and pg_restore (Simple, Downtime Required)
Best for:
Small to medium databases (< 500 GB)
Acceptable downtime during migration
Steps
Export the source database:
pg_dump -Fc -h SOURCE_HOST -U USERNAME DBNAME > backup.dump
Upload backup file to your GCS bucket (optional):
gsutil cp backup.dump gs://BUCKET_NAME/
Restore into Cloud SQL:
pg_restore -h CLOUD_SQL_HOST -U USERNAME -d DBNAME backup.dump
Pros
Simple
Safe
Good for development/staging
Cons
Requires downtime
Not ideal for large datasets
Method 2: Database Migration Service (DMS) — Near Zero Downtime
Best for:
Production workloads
Large databases
Minimal downtime
Google Cloud’s DMS uses replication (logical or continuous) to migrate data with very small cutover time.
Steps
Enable Database Migration Service API in GCP.
Create a Connection Profile for the source PostgreSQL.
Configure network (VPC peering, IP allowlist, or Cloud SQL Auth Proxy).
Create a migration job:
Choose Continuous Migration (CDC-based) for near-zero downtime
Select Cloud SQL PostgreSQL as the destination
Start migration:
DMS copies full initial data
Then streams ongoing changes (inserts/updates/deletes)
Cutover:
Stop application writes to source
Allow DMS to catch up
Promote Cloud SQL as the primary
Pros
Minimal downtime (seconds/minutes)
Fully managed
Handles large-scale migrations
Cons
Requires network setup
Not all extensions supported
Method 3: Physical Replication (Using WAL Files)
Best for:
Very large databases
Low-latency private network
Complex replication requirements
Cloud SQL supports external replicas, allowing PostgreSQL WAL-based replication.
Steps
Configure source PostgreSQL with:
wal_level = logical
max_wal_senders = N
Create a Cloud SQL replica referencing the external master.
Allow replication traffic through networking and firewall rules.
Once synced, perform promotion or cutover.
Pros
Very fast for multi-TB migrations
Minimal downtime
Cons
More complex
Requires fine-tuned configuration
3. Post-Migration Steps
After data is migrated:
A. Validate data
Row counts
Checksums
Application-level functional tests
B. Recreate necessary settings
User roles & permissions
Extensions supported by Cloud SQL
Connection pools (e.g., PgBouncer)
C. Performance tuning
Configure:
max_connections
shared_buffers
work_mem
autovacuum settings
D. Switch application endpoints
Update connection strings to point to Cloud SQL using:
Private IP (recommended)
Cloud SQL Auth Proxy
SSL certificates (if using public IP)
4. Tips for a Seamless Migration
1. Use continuous migration for production
Database Migration Service (DMS) is the safest and most reliable for near-zero downtime.
2. Test migration in a staging environment
Dry-run the migration to discover:
Extension incompatibilities
Network latency issues
Application timeout changes
3. Optimize source DB before migration
VACUUM FULL
REINDEX
ANALYZE
This reduces bloat and speeds up migration.
4. Monitor Cloud SQL performance
Use:
Cloud SQL Insights
Query Plans
Slow query logs
5. High-Level Migration Decision Table
Requirement Best Method
Small DB, simple process pg_dump / pg_restore
Large DB, production, minimal downtime DMS continuous migration
Very large DB (multi-TB) requiring WAL replication External replica + physical replication
On-prem to GCP DMS or VPN + export/import
Multi-cloud migration DMS with connectivity setup
Summary
To migrate a PostgreSQL database to Cloud SQL seamlessly:
Prepare the Cloud SQL instance and network access.
Choose the right migration method:
pg_dump/restore for simple migrations
DMS (recommended) for near-zero downtime
External replicas for very large datasets
Validate data and tune the Cloud SQL instance.
Point the application to the new Cloud SQL endpoint.
Done properly, the migration can be smooth, reliable, and nearly downtime-free.
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