Check Database Memory Usage SGA+PGA

UNIX tools which look at UNIX process memory are unable to distinguish between private and shared memory and thus over-report memory usage for Oracle processes.

Check memory usage from Oracle Database

Total memory usage
select sum(bytes)/1024/1024 mb from (select bytes from v$sgastat union all select value bytes from v$sesstat s, v$statname n where n.STATISTIC# = s.STATISTIC# and  n.name = 'session pga memory' );

Process wise listing
select a.sid,value/(1024*1024) "MB",program from v$session a, v$sesstat b where a.sid=b.sid and b.statistic#=(select statistic# from v$statname where name='session pga memory') order by value/(1024*1024) desc ;


source: oracle communities