List out Oracle's undocumented/hidden database parameters.

You can view your database hidden or underscore parameters by running this query:

SELECT x.ksppinm NAME, y.ksppstvl VALUE, ksppdesc DESCRIPTION FROM x$ksppi x, x$ksppcv y WHERE x.inst_id = userenv('Instance')AND y.inst_id = userenv('Instance') AND x.indx = y.indx AND SUBSTR(x.ksppinm,1,1) = '_' ORDER BY 1;