Data Migration - Safe Schema Changes
When to use this skill
- Migrating database schemas and structures
- Transforming data between formats
- Moving data between database systems
- Implementing versioned database migrations
- Handling data transformations during migrations
- Ensuring data integrity and validation
- Planning zero-downtime migrations
- Rolling back failed migrations safely
- Migrating from legacy systems
- Implementing data backfill strategies
- Testing migrations in staging environments
- Creating migration rollback procedures
When to use this skill
- Migrating data between schemas, zero-downtime deployments.
- When working on related tasks or features
- During development that requires this expertise
Use when: Migrating data between schemas, zero-downtime deployments.
Process
- Add new column
- Dual-write to old & new
- Backfill historical data
- Switch reads to new column
- Remove old column
Example
```sql -- Step 1: Add column ALTER TABLE users ADD COLUMN email_new VARCHAR(255);
-- Step 2: Backfill UPDATE users SET email_new = email WHERE email_new IS NULL;
-- Step 3: Swap ALTER TABLE users DROP COLUMN email; ALTER TABLE users RENAME COLUMN email_new TO email; ```