概述

Oracle系统中有一类参数称之为隐藏参数，是系统中使用，但Oracle官方没有公布的参数，11g中共有2562 左右隐藏参数，这些参数可能是那些还没有成熟或者是系统开发中使用的参数。这些参数在所有Oracle官方提供的文档中都没有介绍，他们的命名有一个共同特征就是都以 '_' 作为参数的首字符。当然这部分的参数是不建议用户进行修改的，除非你对ORACLE的整体架构相当熟悉，对整个参数修改所带来的影响有个清晰的认识。

查看隐藏参数

如：查看_optimizer_adaptive_cursor_sharing

SELECT i.ksppinm name, 
 i.ksppdesc description, 
 CV.ksppstvl VALUE, 
 CV.ksppstdf isdefault
 FROM sys.x$ksppi i, sys.x$ksppcv CV 
 WHERE i.inst_id = USERENV ('Instance') 
 AND CV.inst_id = USERENV ('Instance') 
 AND i.indx = CV.indx 
 AND i.ksppinm ='_optimizer_adaptive_cursor_sharing'
ORDER BY REPLACE (i.ksppinm, '_', '');

11G常见的隐藏参数说明

ORACLE 11GR2常用参数(含隐含参数)设置如下：

alter system set "_PX_use_large_pool" = true scope=spfile;
alter system set "_clusterwide_global_transactions" = false scope=spfile;
alter system set "_gc_defer_time" = 3 scope=spfile;
alter system set "_resource_manager_always_off" = true scope=spfile;
alter system set "_resource_manager_always_on" = false scope=spfile;
alter system set "_serial_direct_read" = never scope=spfile;
alter system set "_cleanup_rollback_entries" = 400 scope=spfile;
alter system set "_optimizer_use_feedback" = false scope=spfile;
alter system set "_dbms_sql_security_level" =0 scope=spfile;
alter system set "_bloom_pruning_enabled" = false scope=spfile;
alter system set "_gc_policy_time" = 0 scope=spfile;
alter system set "_bloom_filter_enabled" = false scope=spfile;
alter system set "_gc_read_mostly_locking" = false scope=spfile;
alter system set "_gc_undo_affinity" = false scope=spfile;
alter system set "_smu_debug_mode" = 134217728 scope=spfile;
alter system set "_undo_autotune" = false scope=spfile;
alter system set deferred_segment_creation = false scope=spfile;
alter system set Audit_trail = none scope=spfile;
alter system set event='28401 trace name context forever,level 1' scope=spfile;
alter system set "_optimizer_extended_cursor_sharing_rel"=none;
alter system set "_optimizer_extended_cursor_sharing"=none;
alter system set "_optimizer_adaptive_cursor_sharing"=false;

篇幅有限，Oracle隐藏参数就介绍到这了，大家感兴趣的话也可以测试研究一下。后面小编会分享更多DBA方面的内容，感兴趣的朋友走一波关注哩~