Undocumented/Hidden Parameters in Oracle 11g

Oracle contains two type of initialization parameters i.e,

1.) Documented Initialization Parameter.
2.) Undocumented Initialization Parameter. 

Here, We will check about the  undocumented Initialization Parameter .

Undocumented Initialization parameter are also called hidden Parameter and there is no document available about these parameter . Every version of Oracle has special undocumented initialization parameters. These undocumented initialization parameters are usually only used in emergencies or with the express consent of Oracle technical support.

The X$KSPPI table contains all of the parameters that influence the oracle database in operation.  X$tables are available only when we connect to the oracle instance as the user 'SYS' .                               

The current version i.e, Oracle 11g has 2394 parameters, out of which 343 parameters are listed in the V$parameter view. This means that there are still 2051 parameters which are not listed in either V$views or Oracle Documentation . Hidden parameter starts with underscore sign  "_"  . To check all initialization  parameter fire below command.

SQL> select count(*) from X$KSPPI;
  COUNT(*)
----------
      2394

To check documented parameter fire the following comand .

SQL> select count(*) from v$parameter;
  COUNT(*)
----------
       343

Here we will discuss when to use hidden parameter , where to use them, and what tricks are involved in using them. Some issues involved with using these parameters are listed below :

1.) Undocumented parameters change from version to version (even in the same versions from patchset to patchset) without any notice. These parameters are not consistent across versions.

2.) All these parameters may not be available with all the ports. This means that they are not compatible across the operating systems. A few parameters are Operating System specific.

3.) Use of undocumented parameters without the knowledge of Oracle Support is a violation of the Support agreement with Oracle. Oracle Worldwide support has every right to refuse to support the databases affected by using these parameters.

4.) A few parameters can potentially corrupt the databases and some parameters within those few will help us in bringing up the corrupted database with minimal data loss. So these parameters are equally useful inspite of those dangers.

5.) Since no external documentation is available, it is important to test them before using these parameters in our production system. It is also suggested to have a complete backup before using these parameters.

We can obtain all the undocumented Parameter i.e, hidden Parameter by giving the following command .

SQL> select a.ksppinm name, b.ksppstvl value,b.ksppstdf deflt,

decode (a.ksppity, 1,

'boolean', 2,

'string', 3,

'number', 4,

'file', a.ksppity) type, a.ksppdesc description

from

sys.x$ksppi a,

sys.x$ksppcv b

where   a.indx = b.indx

   and

a.ksppinm like '\_%' escape '\'

order by name

We can also check the hidden and non-hidden parameter from memory by creating pfile .The command for creating the pfile is 

SQL> Create pfile='C:\pfile.ora'  from memory;

The above command  will not work in case of 10g or lower version of oracle. In my case the content of  pfile created from memory is as :

__db_cache_size=104M

__java_pool_size=4M

__large_pool_size=4M

__oracle_base='D:\oracle' # ORACLE_BASE set from environment

__pga_aggregate_target=132M

__sga_target=196M

__shared_io_pool_size=0

__shared_pool_size=76M

__streams_pool_size=0

_aggregation_optimization_settings=0

_always_anti_join='CHOOSE'

_always_semi_join='CHOOSE'

_and_pruning_enabled=TRUE

_b_tree_bitmap_plans=TRUE

_bloom_filter_enabled=TRUE

_bloom_folding_enabled=TRUE

_bloom_pruning_enabled=TRUE

_complex_view_merging=TRUE

_compression_compatibility='11.2.0.0.0'

_connect_by_use_union_all='TRUE'

_convert_set_to_join=FALSE

_cost_equality_semi_join=TRUE

_cpu_to_io=0

_dimension_skip_null=TRUE

_eliminate_common_subexpr=TRUE

_enable_type_dep_selectivity=TRUE

_fast_full_scan_enabled=TRUE

_first_k_rows_dynamic_proration=TRUE

_gby_hash_aggregation_enabled=TRUE

_generalized_pruning_enabled=TRUE

_globalindex_pnum_filter_enabled=TRUE

_gs_anti_semi_join_allowed=TRUE

_improved_outerjoin_card=TRUE

_improved_row_length_enabled=TRUE

_index_join_enabled=TRUE

_ksb_restart_policy_times='0'

_ksb_restart_policy_times='60'

_ksb_restart_policy_times='120'

_ksb_restart_policy_times='240' # internal update to set default

_left_nested_loops_random=TRUE

_local_communication_costing_enabled=TRUE

_minimal_stats_aggregation=TRUE

_mmv_query_rewrite_enabled=TRUE

_new_initial_join_orders=TRUE

_new_sort_cost_estimate=TRUE

_nlj_batching_enabled=1

_optim_adjust_for_part_skews=TRUE

_optim_enhance_nnull_detection=TRUE

_optim_new_default_join_sel=TRUE

_optim_peek_user_binds=TRUE

_optimizer_adaptive_cursor_sharing=TRUE

_optimizer_better_inlist_costing='ALL'

_optimizer_cbqt_no_size_restriction=TRUE

_optimizer_coalesce_subqueries=TRUE

_optimizer_complex_pred_selectivity=TRUE

_optimizer_compute_index_stats=TRUE

_optimizer_connect_by_combine_sw=TRUE

_optimizer_connect_by_cost_based=TRUE

_optimizer_connect_by_elim_dups=TRUE

_optimizer_correct_sq_selectivity=TRUE

_optimizer_cost_based_transformation='LINEAR'

_optimizer_cost_hjsmj_multimatch=TRUE

_optimizer_cost_model='CHOOSE'

_optimizer_dim_subq_join_sel=TRUE

_optimizer_distinct_agg_transform=TRUE

_optimizer_distinct_elimination=TRUE

_optimizer_distinct_placement=TRUE

_optimizer_eliminate_filtering_join=TRUE

_optimizer_enable_density_improvements=TRUE

_optimizer_enable_extended_stats=TRUE

_optimizer_enhanced_filter_push=TRUE

_optimizer_extend_jppd_view_types=TRUE

_optimizer_extended_cursor_sharing='UDO'

_optimizer_extended_cursor_sharing_rel='SIMPLE'

_optimizer_extended_stats_usage_control=224

_optimizer_fast_access_pred_analysis=TRUE

_optimizer_fast_pred_transitivity=TRUE

_optimizer_filter_pred_pullup=TRUE

_optimizer_fkr_index_cost_bias=10

_optimizer_group_by_placement=TRUE

_optimizer_improve_selectivity=TRUE

_optimizer_join_elimination_enabled=TRUE

_optimizer_join_factorization=TRUE

_optimizer_join_order_control=3

_optimizer_join_sel_sanity_check=TRUE

_optimizer_max_permutations=2000

_optimizer_mode_force=TRUE

_optimizer_multi_level_push_pred=TRUE

_optimizer_native_full_outer_join='FORCE'

_optimizer_new_join_card_computation=TRUE

_optimizer_null_aware_antijoin=TRUE

_optimizer_or_expansion='DEPTH'

_optimizer_order_by_elimination_enabled=TRUE

_optimizer_outer_to_anti_enabled=TRUE

_optimizer_push_down_distinct=0

_optimizer_push_pred_cost_based=TRUE

_optimizer_rownum_bind_default=10

_optimizer_rownum_pred_based_fkr=TRUE

_optimizer_skip_scan_enabled=TRUE

_optimizer_sortmerge_join_inequality=TRUE

_optimizer_squ_bottomup=TRUE

_optimizer_star_tran_in_with_clause=TRUE

_optimizer_system_stats_usage=TRUE

_optimizer_table_expansion=TRUE

_optimizer_transitivity_retain=TRUE

_optimizer_try_st_before_jppd=TRUE

_optimizer_undo_cost_change='11.2.0.1'

_optimizer_unnest_corr_set_subq=TRUE

_optimizer_unnest_disjunctive_subq=TRUE

_optimizer_use_cbqt_star_transformation=TRUE

_optimizer_use_feedback=TRUE

_or_expand_nvl_predicate=TRUE

_ordered_nested_loop=TRUE

_parallel_broadcast_enabled=TRUE

_partition_view_enabled=TRUE

_pivot_implementation_method='CHOOSE'

_pre_rewrite_push_pred=TRUE

_pred_move_around=TRUE

_push_join_predicate=TRUE

_push_join_union_view=TRUE

_push_join_union_view2=TRUE

_px_minus_intersect=TRUE

_px_pwg_enabled=TRUE

_px_ual_serial_input=TRUE

_query_rewrite_setopgrw_enable=TRUE

_remove_aggr_subquery=TRUE

_replace_virtual_columns=TRUE

_right_outer_hash_enable=TRUE

_selfjoin_mv_duplicates=TRUE

_sql_model_unfold_forloops='RUN_TIME'

_sqltune_category_parsed='DEFAULT' # parsed sqltune_category

_subquery_pruning_enabled=TRUE

_subquery_pruning_mv_enabled=FALSE

_system_trig_enabled=FALSE

_table_scan_cost_plus_one=TRUE

_undo_autotune=FALSE

_union_rewrite_for_gs='YES_GSET_MVS'

_unnest_subquery=TRUE

_use_column_stats_for_function=TRUE

aq_tm_processes=0

audit_file_dest='D:\ORACLE\ADMIN\INDIA\ADUMP'

audit_trail='DB'

compatible='11.2.0.0.0'

control_files='D:\ORACLE\ORADATA\INDIA\CONTROL01.CTL'

control_files='D:\ORACLE\FLASH_RECOVERY_AREA\INDIA\CONTROL02.CTL'

core_dump_dest='d:\oracle\diag\rdbms\india\india\cdump'

db_block_size=8192

db_domain=''

db_name='india'

db_recovery_file_dest='D:\oracle\flash_recovery_area'

db_recovery_file_dest_size=4977M

diagnostic_dest='D:\ORACLE'

dispatchers='(PROTOCOL=TCP) (SERVICE=indiaXDB)'

enable_ddl_logging=FALSE

log_buffer=6029312 # log buffer update

memory_target=328M

open_cursors=300

optimizer_dynamic_sampling=2

optimizer_mode='ALL_ROWS'

plsql_warnings='DISABLE:ALL' # PL/SQL warnings at init.ora

processes=150

query_rewrite_enabled='TRUE'

recyclebin='OFF'

remote_login_passwordfile='EXCLUSIVE'

resource_manager_plan=''

result_cache_max_size=864K

skip_unusable_indexes=TRUE

undo_retention=900

undo_tablespace='UNDOTBS1' 

Enjoy   :-)