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Before 2.1.0, we were setting max_connections, max_worker_processes and some other config params to match the source (primary), looking at pg_controldata. Example:

/usr/lib/postgresql/13/bin/pg_controldata -D .. | grep setting
wal_level setting:                    replica
wal_log_hints setting:                off
max_connections setting:              300
max_worker_processes setting:         16
max_wal_senders setting:              10
max_prepared_xacts setting:           0
max_locks_per_xact setting:           64
track_commit_timestamp setting:       off

In 2.1.0 this doesn't work – I've got errors related to max_connections being lower than on the primary, same for max_worker_processes, etc. Example:

... hot standby is not possible because max_worker_processes = 8 is a lower setting than on the master server (its value was 16)