tcn was added in PostgreSQL 9.2.
tcn is useful for applications using drivers which support asynchronous notification: this makes it possible to notify all clients if the contents of a table have been changed, enabling them to take appropriate action in near-real time, such as updating a table cache or information display.
tcn provides a single function,
triggered_change_notification(), to be added as a row-level trigger.
With the exception of bugfixes and minor code changes,
tcn has remained unchanged since it was added in PostgreSQL 9.2.