隐藏参数_high_priority_processes与oradism

运行在操作系统上的进程存在2种系统时序优先级模式:即 实时模式 Real Time(RT) mode, 与分时模式 Time Sharing(TS) mode. 绝大多数Oracle进程运行在TS模式下：

[oracle@rh1 ~]$ ps -efc|grep ora_|grep -v grep
oracle    8510     1 TS   23 Mar27 ?        00:00:02 ora_pmon_PROD
oracle    8512     1 TS   23 Mar27 ?        00:00:00 ora_psp0_PROD
oracle    8514     1 TS   23 Mar27 ?        00:00:00 ora_mman_PROD
oracle    8516     1 TS   23 Mar27 ?        00:00:02 ora_dbw0_PROD
oracle    8518     1 TS   23 Mar27 ?        00:00:04 ora_lgwr_PROD
oracle    8520     1 TS   23 Mar27 ?        00:00:04 ora_ckpt_PROD
oracle    8522     1 TS   23 Mar27 ?        00:00:08 ora_smon_PROD
oracle    8524     1 TS   23 Mar27 ?        00:00:00 ora_reco_PROD
oracle    8526     1 TS   23 Mar27 ?        00:00:34 ora_cjq0_PROD
oracle    8528     1 TS   23 Mar27 ?        00:00:06 ora_mmon_PROD
oracle    8530     1 TS   24 Mar27 ?        00:00:07 ora_mmnl_PROD
oracle    8538     1 TS   23 Mar27 ?        00:00:00 ora_arc0_PROD
oracle    8540     1 TS   23 Mar27 ?        00:00:00 ora_arc1_PROD
oracle    8548     1 TS   23 Mar27 ?        00:00:00 ora_qmnc_PROD
oracle    8555     1 TS   23 Mar27 ?        00:00:00 ora_q000_PROD
oracle    8559     1 TS   23 Mar27 ?        00:00:00 ora_q001_PROD
oracle   30500     1 TS   23 22:10 ?        00:00:00 ora_j000_PROD

如上所示所有进程均运行在TS模式下且priority均为23|24. Oracle一般不推荐使用RT模式，因为虽然个别进程可以通过这种方式获得更多的CPU资源，但往往系统的瓶颈并非CPU,即尽管CPU使用率高了，但实际系统TPS并未得到提升。 在10gr2版本后RAC中的LMS进程成为唯一一个使用RT模式的Oracle进程，我们可以通过查询参数_high_priority_processes了解相关信息：

SQL> col name format a40
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE
  2   FROM SYS.x$ksppi x, SYS.x$ksppcv y
  3   WHERE x.inst_id = USERENV ('Instance')
  4   AND y.inst_id = USERENV ('Instance')
  5   AND x.indx = y.indx
  6  AND x.ksppinm LIKE '%priority%';

NAME                                     VALUE
---------------------------------------- ----------
_high_priority_processes                 LMS*
_os_sched_high_priority                  1

_high_priority_processes通过进程功能名进行匹配，下面我们将提高LGWR及PMON进程的优先级：

SQL> alter system set "_high_priority_processes"='LMS*|LGWR|PMON' scope=spfile;

System altered.

SQL> startup force;
ORACLE instance started.

Total System Global Area  281018368 bytes
Fixed Size                  2083336 bytes
Variable Size             150996472 bytes
Database Buffers          121634816 bytes
Redo Buffers                6303744 bytes
Database mounted.
Database opened.
SQL> !ps -efc|grep ora_|grep -v grep
oracle   31441     1 RR   41 22:50 ?        00:00:00 ora_pmon_PROD
oracle   31445     1 TS   23 22:50 ?        00:00:00 ora_psp0_PROD
oracle   31447     1 TS   23 22:50 ?        00:00:00 ora_mman_PROD
oracle   31449     1 TS   23 22:50 ?        00:00:00 ora_dbw0_PROD
oracle   31451     1 RR   41 22:50 ?        00:00:00 ora_lgwr_PROD
oracle   31455     1 TS   23 22:50 ?        00:00:00 ora_ckpt_PROD
oracle   31457     1 TS   23 22:50 ?        00:00:00 ora_smon_PROD
oracle   31459     1 TS   22 22:50 ?        00:00:00 ora_reco_PROD
oracle   31461     1 TS   23 22:50 ?        00:00:01 ora_cjq0_PROD
oracle   31463     1 TS   23 22:50 ?        00:00:01 ora_mmon_PROD
oracle   31465     1 TS   24 22:50 ?        00:00:00 ora_mmnl_PROD
oracle   31471     1 TS   24 22:50 ?        00:00:00 ora_p000_PROD
oracle   31473     1 TS   24 22:50 ?        00:00:00 ora_p001_PROD
oracle   31475     1 TS   24 22:50 ?        00:00:00 ora_arc0_PROD
oracle   31477     1 TS   22 22:50 ?        00:00:00 ora_arc1_PROD
oracle   31481     1 TS   23 22:50 ?        00:00:00 ora_qmnc_PROD
oracle   31488     1 TS   23 22:50 ?        00:00:00 ora_q000_PROD
oracle   31490     1 TS   23 22:50 ?        00:00:00 ora_q001_PROD
oracle   31500     1 TS   23 22:50 ?        00:00:00 ora_j000_PROD

好了lgwr和pmon进程也进入实时模式了，同时priority值上升到了41. 注意： Oracle默认仅允许LMS进程（11g中多了VKTM进程）使用RT模式是有它的原因的，所以如果不是Oracle support 推荐，您没有任何修改隐式参数的理由。 其次根据Oracle文档[ID 602419.1]的描述，oradism文件(该文件位于$ORACLE_HOME/bin目录下）不正确的权限将导致RT模式无法被正确使用，该文件默认属于root用户并具有s权限。如下测试：

[oracle@rh1 bin]$ ls -la oradism
-r-sr-s---  1 root oinstall 14931 Mar 11  2008 oradism
[oracle@rh1 bin]$ su - root
Password:
[root@rh1 ~]# chown oracle:oinstall /s01/oracle/product/10.2.0/db_1/bin/oradism
[root@rh1 ~]# exit
logout
[oracle@rh1 bin]$ ls -la oradism
-r-xr-x---  1 oracle oinstall 14931 Mar 11  2008 oradism
[oracle@rh1 bin]$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.4.0 - Production on Sun Mar 28 23:07:03 2010

Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup;
ORACLE instance started.

Total System Global Area  281018368 bytes
Fixed Size                  2083336 bytes
Variable Size             150996472 bytes
Database Buffers          121634816 bytes
Redo Buffers                6303744 bytes
Database mounted.
Database opened.
SQL> col name format a35;
SQL> col value format a10;
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE
  2   FROM SYS.x$ksppi x, SYS.x$ksppcv y
  3   WHERE x.inst_id = USERENV ('Instance')
  4   AND y.inst_id = USERENV ('Instance')
  5   AND x.indx = y.indx
  6  AND x.ksppinm LIKE '%priority%';

NAME                                VALUE
----------------------------------- ----------
_high_priority_processes            LMS*|LGWR|PMON
_os_sched_high_priority             1
SQL> !ps -efc|grep ora_|grep -v grep
oracle   31994     1 TS   23 23:07 ?        00:00:00 ora_pmon_PROD
oracle   31998     1 TS   23 23:07 ?        00:00:00 ora_psp0_PROD
oracle   32000     1 TS   23 23:07 ?        00:00:00 ora_mman_PROD
oracle   32002     1 TS   23 23:07 ?        00:00:00 ora_dbw0_PROD
oracle   32004     1 TS   24 23:07 ?        00:00:00 ora_lgwr_PROD
oracle   32008     1 TS   22 23:07 ?        00:00:00 ora_ckpt_PROD
oracle   32010     1 TS   23 23:07 ?        00:00:00 ora_smon_PROD
oracle   32012     1 TS   22 23:07 ?        00:00:00 ora_reco_PROD
oracle   32014     1 TS   23 23:07 ?        00:00:01 ora_cjq0_PROD
oracle   32016     1 TS   23 23:07 ?        00:00:01 ora_mmon_PROD
oracle   32018     1 TS   24 23:07 ?        00:00:00 ora_mmnl_PROD
oracle   32026     1 TS   24 23:07 ?        00:00:00 ora_arc0_PROD
oracle   32028     1 TS   23 23:07 ?        00:00:00 ora_arc1_PROD
oracle   32032     1 TS   23 23:07 ?        00:00:00 ora_qmnc_PROD
oracle   32045     1 TS   23 23:07 ?        00:00:00 ora_q000_PROD
oracle   32065     1 TS   23 23:08 ?        00:00:00 ora_q001_PROD
oracle   32072     1 TS   23 23:08 ?        00:00:00 ora_j000_PROD

that's great, 显然oradism不仅为Oracle实例提供了内存资源控制功能，还包括了进程优先级分配的权限。 我们应当再次声明hidden parameter不应“滥用”于production environment.