Check the hidden underscore parameters…


col "Parameter" for a50
col "Session Value" for a15
col "Instance Value" for a15

select a.ksppinm "Parameter",
b.ksppstvl "Session Value",
c.ksppstvl "Instance Value"
from x$ksppi a, x$ksppcv b, x$ksppsv c
where a.indx = b.indx and a.indx = c.indx
and substr(ksppinm,1,1)='_'
and lower(a.ksppinm) like lower('%&param%')
order by a.ksppinm;


Setting the parameter:

alter system set "&param." = value scope = &scope. ;


scope is one of the following: “both”, “memory”, “spfile”

To remove completely the hidden parameter from the spfile:

alter system reset "&param." scope=spfile SID='*';