PostgreSQL Connection Usage vs max_connections

SELECT state, count(*) AS sessions,
       max(now() - state_change) AS longest_in_state
FROM pg_stat_activity
WHERE backend_type = 'client backend'
GROUP BY state
ORDER BY sessions DESC;

SELECT count(*) AS used,
       current_setting('max_connections')::int AS max_connections,
       round(100.0 * count(*) / current_setting('max_connections')::int, 1) AS used_pct
FROM pg_stat_activity;