hot_standby is a GUC parameter determining whether queries can be run on a standby.
hot_standby was added in PostgreSQL 9.0.
The default value for
hot_standby has no effect when run on a server which is not in recovery.
hot_standby is set to
off, connections to a standby will fail, e.g.:
psql psql: error: could not connect to server: FATAL: the database system is starting up
and a corresponding entry will be made in the log file:
[2020-09-12 14:17:44 UTC] [unknown] postgres postgres LOCATION: ProcessStartupPacket, postmaster.c:2320