SELECT x.ksppinm name,
y.ksppstvl value,
y.ksppstdf isdefault,
decode(bitand(y.ksppstvf,7),1,'MODIFIED',4,'SYSTEM_MOD','FALSE') ismod,
decode(bitand(y.ksppstvf,2),2,'TRUE','FALSE') isadj
FROM
sys.x$ksppi x,
sys.x$ksppcv y
WHERE
x.inst_id = userenv('Instance') AND
y.inst_id = userenv('Instance') AND
x.indx = y.indx
--and x.ksppinm ='_external_scn_rejection_threshold_hours'
order BY translate(x.ksppinm, ' _', ' ');

SQL> alter system set “_gc_policy_time”=0 scope=spfile sid='*';
System altered.
SQL> alter system set “_gc_undo_affinity”=false scope=spfile sid='*';
System altered.

alter system set “_gc_affinity_limit”=10000000;
alter system set “_gc_affinity_minimum”=10000000;