Oracle希望在数据库主机CPU使用率枯竭时，尽可能让核心的几个后台进程可以最大优先级获取CPU, 当然CPU过高会导致I/O 响应时间变长和网络延迟增加，也会间接影响数据的整体性能。

从Oracle 10g开始是有隐藏参数_high_priority_processes控制哪些进程是高优先级,19c参数中除了_high_priority_processes，还增加了_highest_priority_processes控制高优先级。在10.2版本中，Oracle缺少_high_priority_processes对RAC的核心进程LMS*设置高优先级，在11g版本中对LMS*|VKTM设置高优先级，在19c版本中_highest_priority_processes对VKTM是最高优先级，且提供了更多对LMS*|LM*|LCK0|GCR*|CKPT|DBRM|RMS0|LGWR|CR*|RMV*配置高优先级 。

记得在10.2.0.3前有个bug会导致使用CPU进程过高。最近有客户19c RAC遇到CPU使用率超过90%时GC问题较为突出，在查看LMS时，没有在RT模式的状态引起了注意，在19c中LMS还是有一些变化，下面进行了简单的记录。

在Linux平台上，进程的内核调用模式分为三类：

TS – SCHED_OTHER (SCHED_NORMAL) ，这是分时调度策略，缺省的通用级别；FF – SCHED_FIFO，这是实时调度策略，先进先出；RR – SCHED_RR，实时调度策略，时间片轮转;先看一个正常环境 Oracle 19c RAC 2-nodes on RHEL 7.8db alert log

Starting background process CLMNCLMN started with pid=3, OS id=28714Starting background process PSP0PSP0 started with pid=4, OS id=28731Starting background process IPC02021-03-23 10:07:32.440000 +08:00IPC0 started with pid=5, OS id=29420Starting background process VKTMStarting background process GEN0VKTM started with pid=6, OS id=29445 at elevated (RT) priorityVKTM running at (1)millisec precision with DBRM quantum (100)msStarting background process MMANStarting background process LMD1LMD0 started with pid=23, OS id=29631* Load Monitor used for high load check* New Low - High Load Threshold Range = [130560 - 174080]LMS1 started with pid=26, OS id=29640_29663 at elevated (RT) priorityLMS0 started with pid=24, OS id=29635_29662 at elevated (RT) priorityLMS2 started with pid=28, OS id=29646_29666 at elevated (RT) priorityStarting background process LMD2LMD1 started with pid=36, OS id=29659LMS3 started with pid=30, OS id=29649_29667 at elevated (RT) priorityLMS4 started with pid=32, OS id=29651_29672 at elevated (RT) priorityLMS5 started with pid=34, OS id=29653_29677 at elevated (RT) priorityStarting background process LMD3LMD2 started with pid=37, OS id=29681LMD3 started with pid=38, OS id=29686Starting background process RMS0RMS0 started with pid=39, OS id=29689oracle@anbob_com:/home/oracle>  ps -efc|grep vktmgrid      34874      1 RR   41 Jun03 ?        00:06:20 asm_vktm_+ASM1oracle    42358      1 RR   41 Jun03 ?        00:05:24 ora_vktm_anbob1grid      58462      1 RR   41 Jun03 ?        00:06:18 mdb_vktm_-MGMTDB

Note:

使用ps-c选项查看进程优先级时， vktm是RR mode。

oracle@anbob_com:/home/oracle> ps -efc|grep lmsoracle    35148  90946 TS   19 16:02 pts/3    00:00:00 grep --color=auto lmsoracle    66573      1 TS   19 May21 ?        04:32:32 ora_lms0_anbob1oracle    66576      1 TS   19 May21 ?        04:29:41 ora_lms1_anbob1oracle    66578      1 TS   19 May21 ?        04:26:33 ora_lms2_anbob1oracle    66581      1 TS   19 May21 ?        04:26:51 ora_lms3_anbob1oracle    66586      1 TS   19 May21 ?        04:25:38 ora_lms4_anbob1oracle    66589      1 TS   19 May21 ?        04:28:44 ora_lms5_anbob1oracle    66596      1 TS   19 May21 ?        04:25:44 ora_lms6_anbob1oracle    66599      1 TS   19 May21 ?        04:50:02 ora_lms7_anbob1oracle    66603      1 TS   19 May21 ?        04:22:42 ora_lms8_anbob1oracle    66609      1 TS   19 May21 ?        04:21:31 ora_lms9_anbob1oracle    66615      1 TS   19 May21 ?        04:25:41 ora_lmsa_anbob1oracle    66620      1 TS   19 May21 ?        04:29:43 ora_lmsb_anbob1grid     129022      1 TS   19 May14 ?        00:36:49 asm_lms0_+ASM1

Note:

使用ps-c选项查看进程优先级时，lms还是TS Mode。在12c版本及之前PS也是显示RR mode，如下：

# sqlplus -VSQL*Plus: Release 12.2.0.1.0 Production# ps -eLfc |head -n 1;ps -eLfc|grep lmsUID        PID  PPID   LWP NLWP CLS PRI STIME TTY          TIME CMDgrid     14661     1 14661    1 RR   41  2019 ?        1-08:14:40 asm_lms0_+ASM1oracle   62106     1 62106    1 RR   41  2019 ?        17-22:45:22 ora_lms0_weejar1oracle   62109     1 62109    1 RR   41  2019 ?        18-10:30:26 ora_lms1_weejar1oracle   62111     1 62111    1 RR   41  2019 ?        18-00:13:16 ora_lms2_weejar1oracle   62113     1 62113    1 RR   41  2019 ?        17-22:02:20 ora_lms3_weejar1oracle   62115     1 62115    1 RR   41  2019 ?        17-22:07:53 ora_lms4_weejar1

oracle@anbob_com:/home/oracle> ls -l $ORACLE_HOME/bin/oradism-rwsr-x--- 1 root oinstall 147848 Apr 17 2019 /oracle/app/oracle/product/19c/db_1/bin/oradism

正常。

Note:

For 10gR2 and 11gR1 installations, verify that the oradism executable matches the following ownership and permissions “-rwsr-sr-x 1 root dba oradism” and make sure the lms is running in Real Time mode.

检查Oracle_HOME文件系统挂载点

oracle@anbob_com:/home/oracle> cat /proc/mounts|grep oracle/dev/mapper/fusioncube-oracle /oracle ext4 rw,relatime,stripe=16,data=ordered 0 0

正常。

AWR中LMS

RAC StatisticsBegin	End	Number of Instances:	2	2Number of LMS’s:	12	12Number of realtime LMS’s:	12	12	(0 priority changes)

SQL> select 'LMS', INST_ID,PRIORITY,COUNT(*) TOTAL FROM GV$BGPROCESS where name like 'LMS%' GROUP BY INST_ID,PRIORITY ;'LMS'     INST_ID PRIORITY              TOTAL------ ---------- ---------------- ----------LMS             1 RT                       12LMS             2 RT                       12

种种显示当前LMS进程是RT模式，但PS显示进程还是TS，难道是显示问题？还是Oracle有新特性改变?

答案是的确发生了新变化，从18c开始LMS进程改为线程模式。

oracle@anbob_com:/home/oracle> ps -eLfc |head -n 1;ps -eLfc|grep lmsUID         PID   PPID    LWP NLWP CLS PRI STIME TTY          TIME CMDoracle    66573      1  66573    4 TS   19 May21 ?        00:00:08 ora_lms0_anbob1oracle    66573      1  66580    4 RR   41 May21 ?        03:15:29 ora_lms0_anbob1oracle    66573      1  67219    4 TS   19 May21 ?        00:23:08 ora_lms0_anbob1oracle    66573      1  67240    4 TS   19 May21 ?        00:53:41 ora_lms0_anbob1oracle    66576      1  66576    4 TS   19 May21 ?        00:00:08 ora_lms1_anbob1oracle    66576      1  66582    4 RR   41 May21 ?        03:12:36 ora_lms1_anbob1oracle    66576      1  67270    4 TS   19 May21 ?        00:23:09 ora_lms1_anbob1oracle    66576      1  67301    4 TS   19 May21 ?        00:53:43 ora_lms1_anbob1oracle    66578      1  66578    4 TS   19 May21 ?        00:00:08 ora_lms2_anbob1oracle    66578      1  66591    4 RR   41 May21 ?        03:10:10 ora_lms2_anbob1oracle    66578      1  67339    4 TS   19 May21 ?        00:22:52 ora_lms2_anbob1...

OK.

再看另一个问题环境Oracle 19.4 2-nodes RAC on RHEL 7.5

RAC StatisticsBegin	End	Number of Instances:	2	2Number of LMS’s:	40	40Number of realtime LMS’s:	0	0	(0 priority changes)SQL> select * from v$bgprocess where name like 'LMS%';PADDR              PSERIAL# NAME  DESCRIPTION                      PRIORITY     CON_ID---------------- ---------- ----- -------------------------------- -------- ----------0000001E01B628A0          1 LMS0  global cache service process     TS                00000001E01B65360          1 LMS7  global cache service process     TS                00000001E01B67E20          1 LMSE  global cache service process     TS                00000001E01B6A8E0          1 LMSL  global cache service process     TS                00000001E01B6D3A0          1 LMSS  global cache service process     TS                00000001E01B6FE60          1 LMSZ  global cache service process     TS                00000001E21AC8498          1 LMS3  global cache service process     TS                00000001E21ACAF58          1 LMSA  global cache service process     TS                00000001E21ACDA18          1 LMSH  global cache service process     TS                00000001E21AD04D8          1 LMSO  global cache service process     TS                00000001E21AD2F98          1 LMSV  global cache service process     TS                00000001E41A66B58          1 LMS6  global cache service process     TS                0...

2021-06-03T10:50:19.500768+08:00LMON started with pid=22, OS id=98747Starting background process LMD02021-06-03T10:50:19.527437+08:00LMD0 started with pid=23, OS id=98749Starting background process LMD12021-06-03T10:50:19.528918+08:00* Load Monitor used for high load check* New Low - High Load Threshold Range = [230400 - 307200]2021-06-03T10:50:19.703222+08:00Errors in file /u01/oracle/diag/rdbms/anbob1/anbob11/trace/anbob11_lms0_98751_98758.trc  (incident=873064):ORA-00800: soft external error, arguments: [Set Priority Failed], [LMS0], [Check traces and OS configuration], [Check Oracle document and MOS notes], []Incident details in: /u01/oracle/diag/rdbms/anbob1/anbob11/incident/incdir_873064/anbob11_lms0_98751_98758_i873064.trc2021-06-03T10:50:19.711460+08:00Error attempting to elevate LMS0's priority: no further priority changes will be attempted for this processLMS0 started with pid=24, OS id=98751_987582021-06-03T10:50:19.800751+08:00Errors in file /u01/oracle/diag/rdbms/anbob1/anbob11/trace/anbob11_lmsd_98808_98825.trc  (incident=873065):ORA-00800: soft external error, arguments: [Set Priority Failed], [LMSD], [Check traces and OS configuration], [Check Oracle document and MOS notes], []2021-06-03T10:50:19.815049+08:00Error attempting to elevate LMSD's priority: no further priority changes will be attempted for this processLMSD started with pid=50, OS id=98808_988252021-06-03T10:50:19.924836+08:00LMD1 started with pid=104, OS id=989502021-06-03T10:50:19.924929+08:00Starting background process LMD22021-06-03T10:50:19.944617+08:00Errors in file /u01/oracle/diag/rdbms/anbob1/anbob11/trace/anbob11_lmsb_98797_98815.trc  (incident=873066):ORA-00800: soft external error, arguments: [Set Priority Failed], [LMSB], [Check traces and OS configuration], [Check Oracle document and MOS notes], []2021-06-03T10:50:19.945838+08:00Error attempting to elevate LMSB's priority: no further priority changes will be attempted for this processStarting background process LMD32021-06-03T10:50:19.949748+08:00

Note:

这套环境的LMS进程运行在TS模式，是因为在实例启动时遇到了ORA-800错误[Set Priority Failed]失败了。

检查oradism

oracle@anbob1a:/home/oracle/scripts_oracle$ ls -l $ORACLE_HOME/bin/oradism-rwxr-x--- 1 oracle oinstall 147848 Apr 17 2019 /u01/oracle/product/bin/oradism

对于这个环境的owner和权限都是错的，修正后重启实例就可以解决。

也可以root用户使用chrt在线修改进程为RR mode。

# chrt -r -p 1 [lms pid]

墨天轮原文链接：（复制链接至浏览器或点击LMSn没有运行在RT (real time) 模式 Oracle 19c RAC？ - 墨天轮查看）

关于作者

张维照，云和恩墨技术总监，Oracle ACE-A。2006年起从事数据库管理工作，2009年起从事ORACLE DBA维护工作，十余年来专注于Database 技术和架构的研究，热衷于oracle数据库故障诊断、性能优化、内部原理、新特性的学习与分享，在BLOG分享大量的学习和案例经验。从事过多套TB级省级工商、医疗、交通、人社、政府、电信运营商等行业数据库项目从业经验。