remaining connection slots are reserved for non-replication superuser connections

Use the client tools to connect pg, the connection fails, an error the following error:

FATAL: remaining connection slots are reserved for non-replication superuser connections 

View the database connection status and configuration information

select * from pg_stat_activity where pid<>pg_backend_pid() and state='idle';##pg_backend_pid()的结果是当前会话的pid
select datname,datconnlimit from pg_database ;
select current_setting('max_connections');
select current_setting('superuser_reserved_connections');

　　

Found max_connections parameter is set too low.

Because it is a test environment, it is first connected idle state to kill:

## to all the database kill off all idle sessions 
select pg_terminate_backend (pid) from pg_stat_activity where pid <> pg_backend_pid () and state = 'idle';

 Then modify the value of the parameter max_connections.