POSTGRESQL 获取数据库最大连接数和当前连接数

SELECT 
    setting::int AS max_connections,
    (SELECT count(*) FROM pg_stat_activity) AS current_connections,
    setting::int - (SELECT count(*) FROM pg_stat_activity) AS remaining_connections,
    ROUND((SELECT count(*) FROM pg_stat_activity) * 100.0 / setting::int, 2) AS percent_used
FROM pg_settings
WHERE name = 'max_connections';