PMON Terminating the Instance Due To Error 822

刘泽宇

现象：
On : 12.1.0.2 version, RDBMS

Database crashed and the following error observed in the alert log file.

ERROR
-----------------------
Thu Nov 16 20:31:48 2017
Warning: VKTM detected a time drift.
Time drifts can result in an unexpected behavior such as time-outs. Please check trace file for more details.
Thu Nov 16 20:31:49 2017
Instance Critical Process (pid: 6, ospid: 16813, MMAN) died unexpectedly
Thu Nov 16 20:31:49 2017
System state dump requested by (instance=1, osid=16803 (PMON)), summary=[abnormal instance termination].
System State dumped to trace file /apps/oracle/diag/rdbms/<dbname>/<instance_name>/trace/<instance_name>_diag_16817_20171116203149.trc
Thu Nov 16 20:31:49 2017
PMON (ospid: 16803): terminating the instance due to error 822


原因：
The collected OS error log shows "Out of memory" and "Free swap = 0kB" errors, and it proved that mman process got killed due to "Out of memory" problem:
Nov 16 20:31:45 <osname> kernel: Free swap = 0kB <<< Free swap = 0kB
Nov 16 20:31:45 <osname> kernel: Out of memory: Kill process 16813 (ora_mman_<instance_name>) score 112 or sacrifice child <<< Out of memory


处理方法：
Engage OS admin to investigate the memory shortage problem.
The OOM killer, a feature enabled by default, is a self protection mechanism employed by the Linux kernel when under severe memory pressure. Please refer the below document for more details:
Linux: Out-of-Memory (OOM) Killer (Doc ID 452000.1)