DB Statistic Queries
Show max or active connections to PostgreSQL, MySQL
PostgreSQL
The number of max connections
SHOW max_connections;
The number of currently open connections
SELECT sum(numbackends) FROM pg_stat_database;
MySQL
The number of max connections
SHOW GLOBAL VARIABLES LIKE 'max_connections';
The number of currently open connections
SHOW status WHERE `variable_name` = 'Threads_connected';