select count(1) from pg_stat_activity;

show max_connections;

max_connections = 500

//查看过期连接
select * from pg_stat_activity where state = 'idle'
 
//删除连接，括号里传pid
select pg_terminate_backend(25800);
 
//查看最大连接数
show max_connections;
 
//修改最大连接数，需要superuser权限
alter system set max_connections= 1000;