Check current PGA and SGA :
show parameter sga; show parameter pga;
Show current and maximum sessions :
SELECT 'Currently, ' || (SELECT COUNT(*) FROM V$SESSION) || ' out of ' || VP.VALUE || ' connections are used.' AS USAGE_MESSAGE FROM V$PARAMETER VP WHERE VP.NAME = 'sessions';
AWR Retention period :
select snap_interval, retention from dba_hist_wr_control;