今天丑时，BI的一个数据库挂了，早上到公司同事已经修复好了，告警日志显示的问题是Instance terminated by LGWR。

Wed Dec 06 02:34:59 2017
Errors in file /u01/app/oracle/diag/rdbms/ivlstd3/ivlstd3/trace/ivlstd3_lgwr_40339.trc:
ORA-04021: timeout occurred while waiting to lock object
LGWR (ospid: 40339): terminating the instance due to error 4021
Wed Dec 06 02:34:59 2017
opiodr aborting process unknown ospid (50722) as a result of ORA-1092
Wed Dec 06 02:35:00 2017
System state dump requested by (instance=1, osid=40339 (LGWR)), summary=[abnormal instance termination].
System State dumped to trace file /u01/app/oracle/diag/rdbms/ivlstd3/ivlstd3/trace/ivlstd3_diag_40315_20171206023500.trc
Instance terminated by LGWR, pid = 40339

这是一个物理备库(ADG)，数据库版本是11.2.0.4.0 for linux 64bit，操作系统使用的是OEL 6.5，同事启动这个备库并且启动MRP进程的时候，只是遇到了GAP，把日志传过来后，一切正常。

通过MOS查询，发现这可能是ADG的BUG，解决方法是修改_adg_parselock_timeout隐含参数，下面是MOS的文章信息。

APPLIES TO:
Oracle Database - Enterprise Edition - Version 11.2.0.4 and later
Information in this document applies to any platform.
SYMPTOMS
ORA-04021: timeout occurred while waiting to lock object

CAUSE
Bug 18242740?ACTIVE STANDBY DATABASE CRASHED WITH ORA-4021 closed as duplicate of?Bug 17018214?- ORA-600 [KRDRSB_END_QSCN_2]
SOLUTION
Fix is already included in 11.2.0.4 but the fix is DISABLED by default.
To enable the fix ?set "_adg_parselock_timeout" to the number of centi-seconds LGWR should wait before backing off and retrying the request.
Set ?the parameter "_adg_parselock_timeout"?

On the Active Data Guard Standby set below parameter and restart standby:
ALTER SYSTEM set "_adg_parselock_timeout"=550 scope=both;

本文固定链接: https://www.dbdream.com.cn/2017/12/oracle-11g-adg%e9%81%87%e5%88%b0instance-terminated-by-lgwr/ | 信春哥，系统稳，闭眼上线不回滚！