I came across an interesting article written in Chinese on itpub.net. That article shows how to use sql*plus command "Show Parameter" to show hidden init parameters of Oracle.
Please note: Never do it on your production database because it may cause your database corrupt. The original practice was done against Oracle 9ir2, the practice below is done against Oracle 10gr1.Oracle hidden (undocumented) init parameters are critical for oracle database. And, it should be protected against update unless Oracle support allow you to do that. Therefore, these hidden init parameters are invisible for database DBAs and Developers. To view to value of hidden init parameters, those who are interested in studying Oracle internal usually rely on scripts to display those hidden init parameters.
The question is: Can we check the value of hidden init parameters by using common sql*plus command "show parameters"? The answer is: Absolutely Yes. Now, we'd like to show how to do that step by step.
Step 1: Find internal of "show parameter" by session tracing**********************************************************************************
SQL> alter session set sql_trace=true;
SQL> show parameter optimizer
NAME TYPE VALUE
------------------------------------------------------------------------------------------------------
optimizer_dynamic_sampling integer 2
optimizer_features_enable string 10.1.0
optimizer_index_caching integer 0
optimizer_index_cost_adj integer 100
optimizer_mode string ALL_ROWS
SQL> exit
**********************************************************************************
Step 2: Find internal sql statement in trace file
The major statement in trace file looks like following:
**********************************************************************************
SELECT NAME NAME_COL_PLUS_SHOW_PARAM,
DECODE(TYPE,1,'boolean',2,'string',3,'
integer',4,'file',5,'number', 6,'big integer', 'unknown')
TYPE,DISPLAY_VALUE VALUE_COL_PLUS_SHOW_PARAM
FROM V$PARAMETER
WHERE UPPER(NAME) LIKE UPPER('%optimizer%')
ORDER BY NAME_COL_PLUS_SHOW_PARAM,ROWNUM
**********************************************************************************
It's clear that "show parameter" actually make query on view v$parameter.
Step 3: Examing definition of view v$parameter
**********************************************************************************
SQL> SELECT * FROM v$fixed_view_definition
WHERE view_name = 'V$PARAMETER';
VIEW_NAME VIEW_DEFINITION
----------------------------------------------------------------------------------------------------
V$PARAMETER select NUM , NAME , TYPE , VALUE , DISPLAY_VALUE,
ISDEFAULT , ISSES_MODIFIABLE ,
ISSYS_MODIFIABLE ,
ISINSTANCE_MODIFIABLE,
ISMODIFIED , ISADJUSTED , ISDEPRECATED,
DESCRIPTION, UPDATE_COMMENT, HASH
from GV$PARAMETER
where inst_id = USERENV('Instance' )
SQL> SELECT * FROM v$fixed_view_definition WHERE view_name = 'GV$PARAMETER';
VIEW_NAME VIEW_DEFINITION
---------------------------------------------------------------------------------------------------
GV$PARAMETER select x.inst_id,x.indx+1,ksppinm,ksppity,ksppstvl, ksppstdvl,
ksppstdf, decode(bitand(ksppiflg/256,1),1,'TRUE','FALSE'),
decode(bitand(ksppiflg/65536,3),1, 'IMMEDIATE',2,
'DEFERRED',3,'IMMEDIATE','FALSE'),
decode(bitand(ksppiflg,4),4,'FALSE',
decode(bitand(ksppiflg/65536,3), 0, 'FALSE','TRUE')),
decode(bitand(ksppstvf,7),1,'MODIFIED',4,'SYSTEM_MOD',
'FALSE'),
decode(bitand(ksppstvf,2),2,'TRUE','FALSE'),
decode(bitand(ksppilrmflg/64, 1), 1, 'TRUE', 'FALSE'),
ksppdesc, ksppstcmnt, sppihash
from x$ksppi x, x$ksppcv y
where (x.indx = y.indx) and ((translate(ksppinm,'_','#' )not like '#%')
or (ksppstdf = 'FALSE'))
**********************************************************************************
The highlighted red part is key to eliminate hidden init parameters while using "show parameter" (hidden init parameters start with character '_' ).
Step 4: Create pseudo-view of v$paramter
**********************************************************************************
SQL> connect sys@orcl as sysdba
Enter password:
Connected.
SQL> create or replace view my_v$parameter_with_hidden
(NUM,NAME , TYPE, display_Value , ISDEFAULT , ISSES_MODIFIABLE ,
ISSYS_MODIFIABLE ,ISMODIFIED , ISADJUSTED, DESCRIPTION,
UPDATE_COMMENT)
as
select x.indx+1,ksppinm,ksppity,ksppstvl,ksppstdf,
decode(bitand(ksppiflg/256,1),1,'TRUE','FALSE'),
decode(bitand(ksppiflg/65536,3),1,'IMMEDIATE',2,'DEFERRED',
3,'IMMEDIATE','FALSE'), decode(bitand(ksppstvf,7),
1,'MODIFIED',4,'SYSTEM_MOD','FALSE'),
decode(bitand(ksppstvf,2),2,'TRUE','FALSE'),
ksppdesc, ksppstcmnt
from x$ksppi x, x$ksppcv y
where (x.indx = y.indx);
View created.
SQL> grant select on my_v$parameter_with_hidden to system;
Grant succeeded.
SQL> connect system@orcl
Enter password:
Connected.
SQL> create synonym v$parameter for sys.my_v$parameter_with_hidden;
Synonym created.
***************************************************************************
Step 5: able to use "show parameter" to show hidden init parameters
***************************************************************************
SQL> show parameter optimizer
NAME TYPE VALUE
-----------------------------------------------------------------------------------------------
_optimizer_adjust_for_nulls boolean TRUE
_optimizer_autostats_job boolean TRUE
_optimizer_block_size integer 8192
_optimizer_cache_stats boolean FALSE
_optimizer_cbqt_factor integer 50
_optimizer_ceil_cost boolean TRUE
_optimizer_choose_permutation integer 0
_optimizer_compute_index_stats boolean TRUE
_optimizer_correct_sq_selectivity boolean TRUE
_optimizer_cost_based_transformation string LINEAR
_optimizer_cost_filter_pred boolean FALSE
_optimizer_cost_model string CHOOSE
_optimizer_degree integer 0
_optimizer_dim_subq_join_sel boolean TRUE
_optimizer_disable_strans_sanity_che integer 0
cks
_optimizer_dyn_smp_blks integer 32
_optimizer_ignore_hints boolean FALSE
_optimizer_invalidation_period integer 18000
_optimizer_join_order_control integer 3
_optimizer_join_sel_sanity_check boolean TRUE
_optimizer_max_permutations integer 2000
_optimizer_mjc_enabled boolean TRUE
_optimizer_mode_force boolean TRUE
_optimizer_new_join_card_computation boolean TRUE
_optimizer_percent_parallel integer 101
_optimizer_push_down_distinct integer 0
_optimizer_random_plan integer 0
_optimizer_save_stats boolean TRUE
_optimizer_search_limit integer 5
_optimizer_skip_scan_enabled boolean TRUE
_optimizer_sortmerge_join_enabled boolean TRUE
_optimizer_squ_bottomup boolean TRUE
_optimizer_system_stats_usage boolean TRUE
_optimizer_undo_changes boolean FALSE
_optimizer_undo_cost_change string 10.1.0
optimizer_dynamic_sampling integer 2
optimizer_features_enable string 10.1.0
optimizer_index_caching integer 0
optimizer_index_cost_adj integer 100
optimizer_mode string ALL_ROWS
**********************************************************************************
That's it. Again, never do it in production environment!
