$ psql -U postgres -c 'show config_file'
config_file
-----------------------------------------
/path/to/postgresql.conf
shared_preload_libraries = 'pg_stat_statements'
pg_stat_statements.track = all
sudo systemctl restart postgresql
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
SELECT count(*) FROM pg_stat_statements;
psql -U postgres -c 'show max_wal_size'