wal sender
also: replication sender, walsender
A PostgreSQL background process that reads the Write-Ahead Log (WAL) and sends it to standby replicas to keep them synchronized with the primary database server.
A WAL sender is a dedicated PostgreSQL server process that streams transaction log records (WAL segments) from the primary database to one or more replica servers in real time. This ensures replicas stay up-to-date with changes made on the primary.
Each connected replica has its own WAL sender process. The sender reads WAL files sequentially and transmits them over the network, allowing replicas to apply the same transactions and maintain an identical copy of the database.
Example: When you execute INSERT statements on a primary PostgreSQL server configured for streaming replication, the WAL sender automatically ships those changes to standby servers, enabling high availability and read-only replica queries.