What methods can be used to ensure database fault tolerance?

Database fault tolerance is ensured by several methods:

1. Replication — creating copies of data on multiple servers. If one server fails, data is available on another.
2. Clustering — combining multiple servers into a cluster with automatic failover to a backup node in case of failure.
3. Backup (snapshots) — regularly saving data for recovery after failures.
4. Transaction logging (Write-Ahead Logging) — recording changes before applying them, allowing database recovery after an crash.
5. Using distributed databases — data is stored on multiple nodes, increasing resilience.
6. Monitoring and automatic failover — systems that automatically detect failures and switch to backup.

Example: in PostgreSQL, you can set up replication with a hot standby so that in case of primary server failure, requests are redirected to the replica.