Search notes:

Oracle: V$PGASTAT

v$pgastat can be queried for PGA memory usage statistics. 
select
   name,
   case unit
      when 'bytes'   then to_char(value / 1024/1024, '999,990') || ' mb'
      when 'percent' then to_char(value            , '9999990') || ' %'
      else                to_char(value            , '9999990')
   end                                                                 val,
   con_id
from
   v$pgastat
order by
   lower(name);

PGA statistic names

v$pgastat records the following statistics:
aggregate PGA auto target
aggregate PGA target parameter
bytes processed
cache hit percentage
extra bytes read/written
global memory bound
max processes count
maximum MGA allocated
maximum PGA allocated
maximum PGA used for auto workareas
maximum PGA used for manual workareas
MGA allocated (under PGA)
over allocation count
PGA memory freed back to OS
process count The number of processes that were active during the last three seconds.
recompute count (total)
total freeable PGA memory
total PGA allocated
total PGA inuse
total PGA used for auto workareas
total PGA used for manual workareas

See also

Oracle Dynamic Performance Views

Index