In what cases and at what stage is data transferred during system update at the database level?

Data migration during system updates at the database level is usually carried out during the database migration phase. This occurs after developing and testing the new version, before deploying it to production.

Key points:

• When: during the deployment of a new application version that requires changes in data structure or format.
• What: modifying the database schema, transforming or transferring existing data into the new structure.
• How: using migration scripts or migration tools (e.g., Flyway, Liquibase for SQL, or custom scripts for NoSQL).

Example: if a new version adds a new field or changes the storage format, migration transforms old records to match the new structure.

It is important to perform migrations carefully to avoid data loss and ensure compatibility with the current application version during the transition period.