Can you explain the role and working principle of a master in a database replication scheme?

In a database replication scheme, the master (primary) is the main server that handles all write operations (INSERT, UPDATE, DELETE). Its role is to ensure data consistency and propagate changes to replicas (slaves).

Working principle:

• Clients send write requests to the master.
• The master records changes in the transaction log (WAL in PostgreSQL).
• These changes are asynchronously or synchronously transmitted to replicas.
• Replicas apply the changes, maintaining an up-to-date copy of the data.

Thus, the master is responsible for data integrity and serves as the source of truth, while replicas provide read scalability and fault tolerance.