LMSn没有运行在RT (real time) 模式Oracle 19c RAC?
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 7.8
db alert log
Starting background process CLMN
CLMN started with pid=3, OS id=28714
Starting background process PSP0
PSP0 started with pid=4, OS id=28731
Starting background process IPC0
2021-03-23 10:07:32.440000 +08:00
IPC0 started with pid=5, OS id=29420
Starting background process VKTM
Starting background process GEN0
VKTM started with pid=6, OS id=29445 at elevated (RT) priority
VKTM running at (1)millisec precision with DBRM quantum (100)ms
Starting background process MMAN
Starting background process LMD1
LMD0 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) priority
LMS0 started with pid=24, OS id=29635_29662 at elevated (RT) priority
LMS2 started with pid=28, OS id=29646_29666 at elevated (RT) priority
Starting background process LMD2
LMD1 started with pid=36, OS id=29659
LMS3 started with pid=30, OS id=29649_29667 at elevated (RT) priority
LMS4 started with pid=32, OS id=29651_29672 at elevated (RT) priority
LMS5 started with pid=34, OS id=29653_29677 at elevated (RT) priority
Starting background process LMD3
LMD2 started with pid=37, OS id=29681
LMD3 started with pid=38, OS id=29686
Starting background process RMS0
RMS0 started with pid=39, OS id=29689
oracle@anbob_com:/home/oracle> ps -efc|grep vktm
grid 34874 1 RR 41 Jun03 ? 00:06:20 asm_vktm_+ASM1
oracle 42358 1 RR 41 Jun03 ? 00:05:24 ora_vktm_anbob1
grid 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 lms
oracle 35148 90946 TS 19 16:02 pts/3 00:00:00 grep --color=auto lms
oracle 66573 1 TS 19 May21 ? 04:32:32 ora_lms0_anbob1
oracle 66576 1 TS 19 May21 ? 04:29:41 ora_lms1_anbob1
oracle 66578 1 TS 19 May21 ? 04:26:33 ora_lms2_anbob1
oracle 66581 1 TS 19 May21 ? 04:26:51 ora_lms3_anbob1
oracle 66586 1 TS 19 May21 ? 04:25:38 ora_lms4_anbob1
oracle 66589 1 TS 19 May21 ? 04:28:44 ora_lms5_anbob1
oracle 66596 1 TS 19 May21 ? 04:25:44 ora_lms6_anbob1
oracle 66599 1 TS 19 May21 ? 04:50:02 ora_lms7_anbob1
oracle 66603 1 TS 19 May21 ? 04:22:42 ora_lms8_anbob1
oracle 66609 1 TS 19 May21 ? 04:21:31 ora_lms9_anbob1
oracle 66615 1 TS 19 May21 ? 04:25:41 ora_lmsa_anbob1
oracle 66620 1 TS 19 May21 ? 04:29:43 ora_lmsb_anbob1
grid 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 -V
SQL*Plus: Release 12.2.0.1.0 Production
# ps -eLfc |head -n 1;ps -eLfc|grep lms
UID PID PPID LWP NLWP CLS PRI STIME TTY TIME CMD
grid 14661 1 14661 1 RR 41 2019 ? 1-08:14:40 asm_lms0_+ASM1
oracle 62106 1 62106 1 RR 41 2019 ? 17-22:45:22 ora_lms0_weejar1
oracle 62109 1 62109 1 RR 41 2019 ? 18-10:30:26 ora_lms1_weejar1
oracle 62111 1 62111 1 RR 41 2019 ? 18-00:13:16 ora_lms2_weejar1
oracle 62113 1 62113 1 RR 41 2019 ? 17-22:02:20 ora_lms3_weejar1
oracle 62115 1 62115 1 RR 41 2019 ? 17-22:07:53 ora_lms4_weejar1
检查oradism文件
oracle@anbob_com:/home/oracle> ls -l $ORACLE_HOME/bin/oradism
-rwsr-x--- 1 root oinstall 147848 Apr 17 2019 /oracle/app/oracle/product/19c/db_1/bin/oradism
正常。
Note:
For 10gR2 and 11gR1 installations, verify that the oradism executable matches the following ownership and permissions “-rwsr-sr-x 1 root dba oradism” and make sure the lms is running in Real Time mode.
检查Oracle_HOME文件系统挂载点
oracle@anbob_com:/home/oracle> cat /proc/mounts|grep oracle
/dev/mapper/fusioncube-oracle /oracle ext4 rw,relatime,stripe=16,data=ordered 0 0
正常。
AWR中LMS
RAC Statistics
BeginEnd
Number of Instances:22
Number of LMS’s:1212
Number of realtime LMS’s:1212(0 priority changes)
检查后台进程
SQL> select 'LMS', INST_ID,PRIORITY,COUNT(*) TOTAL FROM GV$BGPROCESS where name like 'LMS%' GROUP BY INST_ID,PRIORITY ;
'LMS' INST_ID PRIORITY TOTAL
------ ---------- ---------------- ----------
LMS 1 RT 12
LMS 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 lms
UID PID PPID LWP NLWP CLS PRI STIME TTY TIME CMD
oracle 66573 1 66573 4 TS 19 May21 ? 00:00:08 ora_lms0_anbob1
oracle 66573 1 66580 4 RR 41 May21 ? 03:15:29 ora_lms0_anbob1
oracle 66573 1 67219 4 TS 19 May21 ? 00:23:08 ora_lms0_anbob1
oracle 66573 1 67240 4 TS 19 May21 ? 00:53:41 ora_lms0_anbob1
oracle 66576 1 66576 4 TS 19 May21 ? 00:00:08 ora_lms1_anbob1
oracle 66576 1 66582 4 RR 41 May21 ? 03:12:36 ora_lms1_anbob1
oracle 66576 1 67270 4 TS 19 May21 ? 00:23:09 ora_lms1_anbob1
oracle 66576 1 67301 4 TS 19 May21 ? 00:53:43 ora_lms1_anbob1
oracle 66578 1 66578 4 TS 19 May21 ? 00:00:08 ora_lms2_anbob1
oracle 66578 1 66591 4 RR 41 May21 ? 03:10:10 ora_lms2_anbob1
oracle 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 Statistics
BeginEnd
Number of Instances:22
Number of LMS’s:4040
Number of realtime LMS’s:00(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 0
0000001E01B65360 1 LMS7 global cache service process TS 0
0000001E01B67E20 1 LMSE global cache service process TS 0
0000001E01B6A8E0 1 LMSL global cache service process TS 0
0000001E01B6D3A0 1 LMSS global cache service process TS 0
0000001E01B6FE60 1 LMSZ global cache service process TS 0
0000001E21AC8498 1 LMS3 global cache service process TS 0
0000001E21ACAF58 1 LMSA global cache service process TS 0
0000001E21ACDA18 1 LMSH global cache service process TS 0
0000001E21AD04D8 1 LMSO global cache service process TS 0
0000001E21AD2F98 1 LMSV global cache service process TS 0
0000001E41A66B58 1 LMS6 global cache service process TS 0
...
db alert log
2021-06-03T10:50:19.500768+08:00
LMON started with pid=22, OS id=98747
Starting background process LMD0
2021-06-03T10:50:19.527437+08:00
LMD0 started with pid=23, OS id=98749
Starting background process LMD1
2021-06-03T10:50:19.528918+08:00
* Load Monitor used for high load check
* New Low - High Load Threshold Range = [230400 - 307200]
2021-06-03T10:50:19.703222+08:00
Errors 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.trc
2021-06-03T10:50:19.711460+08:00
Error attempting to elevate LMS0's priority: no further priority changes will be attempted for this process
LMS0 started with pid=24, OS id=98751_98758
2021-06-03T10:50:19.800751+08:00
Errors 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+08:00
Error attempting to elevate LMSD's priority: no further priority changes will be attempted for this process
LMSD started with pid=50, OS id=98808_98825
2021-06-03T10:50:19.924836+08:00
LMD1 started with pid=104, OS id=98950
2021-06-03T10:50:19.924929+08:00
Starting background process LMD2
2021-06-03T10:50:19.944617+08:00
Errors 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+08:00
Error attempting to elevate LMSB's priority: no further priority changes will be attempted for this process
Starting background process LMD3
2021-06-03T10:50:19.949748+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]