How to set or unset a hidden parameter
Summary
Displays a list of one or all the hidden parameters.
SELECT a.ksppinm AS parameter,
a.ksppdesc AS description,
b.ksppstvl AS session_value,
c.ksppstvl AS instance_value
FROM x$ksppi a,
x$ksppcv b,
x$ksppsv c
WHERE a.indx = b.indx
AND a.indx = c.indx
AND a.ksppinm LIKE '/_%' ESCAPE '/'
--AND a.ksppinm = DECODE(LOWER('&1'), 'all', a.ksppinm, LOWER('&1'))
ORDER BY a.ksppinm;
The query returns 603 hidden parameters for Oracle9i
Display all the DESUPPORTED parameters
SELECT kspponm NAME,
DECODE(ksppoflg,1,'DESUPPORTED','UNDERSCORE') SETTING
FROM x$ksppo
WHERE ksppoflg = 1
ORDER BY NAME ASC;
To set a hidden parameter issue
ALTER SYSTEM SET "_log_io_size"= 1048576 SCOPE = SPFILE;
To unset a parameter issue
ALTER SYSTEM RESET db_block_buffers SCOPE=SPFILE SID='*';
To see which hidden parameters have been set issue
SELECT * FROM v$parameter WHERE SUBSTR(NAME, 0,1) ='_';