Can you explain the principle of data replication in a database?

Data replication in a database is the process of copying and maintaining data consistency across multiple servers (replicas). The main goal is to improve fault tolerance, scalability, and data availability.

Working principle:

• Master-Slave (leader-follower): one database (master) accepts records and updates, while others (slaves) receive copies of data and apply changes.
• Logical or physical replication: changes can be transmitted as SQL queries (logical) or as binary data (physical).
• Change transmission: the master records changes in a transaction log (WAL), which is then sent to slaves.
• Asynchronous or synchronous replication: in asynchronous mode, slaves may lag behind; in synchronous mode, a write is considered successful only after confirmation from slaves.

Example: in PostgreSQL, the master writes changes to WAL, slaves read the WAL and apply changes, maintaining an up-to-date copy of the database.

Thus, replication provides data backup and load distribution for read operations.