How to check if your PostgreSQL server is part of a replication setup

If the server is down, check the entries in postgresql.auto.conf.

The following postgres.auto.conf is from a slave server:

wal_level = 'replica'
hot_standby = on
hot_standby_feedback = 'on'
primary_slot_name = 'stby1'
max_connections = 636

primary_conninfo      = 'host=pgserver01.oric.no port=5432 user=replicate password=mysecretpassword'
promote_trigger_file  = '/tmp/MasterNow'

The master server may have a very simple postgres.auto.conf file:

# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
wal_level = 'replica'

If the server is up, use queries:

1. On the primary server, check that data is shipped over to the replica server:

[postgres@pgserver01.oric.no /pgdata/data]$ echo 'select usename,state,sync_state,sync_priority,client_hostname from pg_stat_replication;' | psql
  usename  |   state   | sync_state | sync_priority |        client_hostname
-----------+-----------+------------+---------------+--------------------------------
 replicate | streaming | async      |             0 | pgserver02.oric.no
(1 row)

2. The following query should return f (false) on primary server, t (true) on the replica server:

[postgres@pgserver01 /pgdata/data/log]$ echo "select pg_is_in_recovery();" | psql
 pg_is_in_recovery
-------------------
 f
(1 row)

[postgres@pgserver02 /pgdata/data/log]$  echo "select pg_is_in_recovery();" | psql
 pg_is_in_recovery
-------------------
 t
(1 row)