【Trouble Shooting】Oracle ADG hung，出现ORA-04021

异常问题：

突然收到告警，ADG实例状态异常。

环境：

版本：Oracle 11.2.0.4.201020

状态：Active Dataguard

问题：

查看Oracle实例alert日志，发现有异常报错：

Thu Dec 12 22:15:23 2024
Errors in file /app/oracle/diag/rdbms/xxx_cloud/xxx/trace/xxx_lgwr_111105.trc:
ORA-04021: timeout occurred while waiting to lock object
LGWR (ospid: 111105): terminating the instance due to error 4021
Thu Dec 12 22:15:24 2024
System state dump requested by (instance=1, osid=111105 (LGWR)), summary=[abnormal instance termination].
System State dumped to trace file /app/oracle/diag/rdbms/xxx_cloud/xxx/trace/xxx_diag_111085_20241212221524.trc
Dumping diagnostic data in directory=[cdmp_20241212221524], requested by (instance=1, osid=111105 (LGWR)), summary=[abnormal instance termination].
Instance terminated by LGWR, pid = 111105

trace日志：

error 4021 detected in background process
ORA-04021: timeout occurred while waiting to lock object
kjzduptcctx: Notifying DIAG for crash event
----- Abridged Call Stack Trace -----
ksedsts()+465<-kjzdssdmp()+267<-kjzduptcctx()+232<-kjzdicrshnfy()+63<-ksuitm()+1312<-ksbrdp()+3507<-opirip()+623<-opidrv()+603<-sou2o()+103<-opimai_real()+250<-ssthrdmain()+265<-main()+201<-__libc_start_main()+245
----- End of Abridged Call Stack Trace -----

分析：

查看mos，异常原因为bug引发：

Bug 16717701 - ADG SHOULD GET THE INSTANCE PARSE LOCK WITH A TIMEOUT  ------> Superseded By Bug fix Bug 17018214

Bug 11712267 - ACTIVE DATA GUARD DATABASE HUNG ON 'LIBRARY CACHE: MUTEX X' WAIT EVENT

解决方案：

修改隐含参数：

alter system set "_adg_parselock_timeout"=500 scope=both sid='*';