Detect PG configuration difference between 2 servers

[Krysztophe]

Original use case: configuration was changed on the primary, not copied on the replica. After the restart, the replica does not even start (different max_connections). Or the replica behaves differently than the old primary after a failover.

''settings'' or ''configuration'' services raise alerts when the conf changes or there is something pending, but this is not enough.

Need: a check that raises an alert when the configuration is or will be different on 2 (or more!) servers. These are not always primary/replicas (eg. sharding). Critical could be raised for incoherences preventing a restart (eg. max_connections).

Exclusion/exclusion of parameters would allow some flexibility. Some parameters could be excluded by default (eg. cluster_name, perhaps log_* ?)

Option 1) Compare ''pg_settings'' values. This works only after a ''pg_reload_conf()'', so some configuration can be forgotten . This does not work on a replica which is already down.

Option 2) Get the parameters from postgresql.conf/auto.conf. This is painful due to included files. ''postgres -C'' is very nice for this but need to be provided with the parameter name; AFAIK you cannot get the whole configuration this way. And this needs a filesystem access, some rights, and to define binary & PGDATA paths.

Perhaps is there place for 2 services? compare_active_conf and compare_restart_conf ?

[Krysztophe]

For option 2, pg_file_settings would be helpful