Query the database maximum number of connections

// current database connections 
SELECT COUNT (* ) from V $ Process; 
// Maximum number of database connections 
SELECT WHERE value from V $ Parameter name = 'Processes'; 
// modify the maximum number of connections: 1000 
ALTER SET System Processes = 1000 = SPFILE scope; 
// current number of sessions 
select count (*) from v $ session; 
the maximum number of sessions // 
select value from v $ parameter where name = 'sessions';