Streaming replication (physical replication), which is byte-by-byte replication, involves a continuous application of WAL records from Primary to Standby. As it uses a file-based log shipping method, it is one of the fastest replication methods when compared with logical replication or other trigger-based methods. It is asynchronous by default. For every replica/standby, there exists a WAL sender process on the primary server and a WAL receiver process on the standby server in streaming replication. These processes are responsible for streaming and applying the WAL records from the WAL segments, including the segments that are not full.
Starting from PostgreSQL 13, there have been some changes in how we perform streaming replication. For example, we don't see a recovery.conf file with PostgreSQL 13, unlike version 11 and earlier. Instead, the parameters that were initially added to recovery.conf can now be set in postgresql.conf...