How are relational databases backed up?

Relational databases are typically backed up using a combination of logical and physical backup methods, depending on the database system and requirements. A logical backup involves exporting the database structure and data into a portable format like SQL statements or CSV files. For example, tools like mysqldump for MySQL or pg_dump for PostgreSQL generate SQL scripts that can recreate the database. Physical backups, on the other hand, copy the raw database files (e.g., data files, transaction logs) from the storage system. This method is faster for large databases but is often tied to the specific database version and storage setup. Both approaches require careful planning to ensure data consistency during the backup process.

The choice between logical and physical backups depends on factors like database size, recovery time objectives, and infrastructure. Logical backups are portable and useful for smaller datasets or schema migrations but can become slow for terabytes of data. Physical backups are more efficient for large-scale systems but may require the database to be temporarily offline or in a consistent state (e.g., using FLUSH TABLES WITH READ LOCK in MySQL). Many databases also support incremental backups, which only capture changes since the last backup. For instance, PostgreSQL’s Write-Ahead Logging (WAL) allows continuous archiving of transaction logs, enabling point-in-time recovery. Cloud-managed databases like Amazon RDS automate backups by combining snapshots (physical) and transaction log retention (incremental).

Backup strategies must also address data integrity and redundancy. A common practice is to use a combination of full backups (weekly) and incremental/differential backups (daily). For example, SQL Server supports full, differential, and transaction log backups, which can be restored in sequence to recover data. Backups should be stored offsite or in cloud storage, adhering to the 3-2-1 rule (three copies, two media types, one offsite). Testing backups through periodic restore drills is critical—tools like mysqlcheck or automated scripts can validate backup consistency. Developers should also consider encryption for sensitive data and monitor backup processes for failures. Ultimately, the method depends on balancing recovery speed, storage costs, and operational complexity for the specific use case.