LGWR (ospid: 29534): terminating the instance due to error 4021

ksuitm: waiting up to [5] seconds before killing DIAG(29522)

公司备库ADG意外宕机，alert日志显示LGWR进程终止了DB instance

Errors in file /app/oracle_11g/diag/rdbms/hkadg/hkadg/trace/hkadg_lgwr_29534.trc:

ORA-04021: timeout occurred while waiting to lock object 

Sun Mar 24 05:53:27 2019

System state dump requested by (instance=1, osid=29534 (LGWR)), summary=[abnormal instance termination].

LGWR (ospid: 29534): terminating the instance due to error 4021

System State dumped to trace file /app/oracle_11g/diag/rdbms/hkadg/hkadg/trace/hkadg_diag_29522_20190324055327.trc

Dumping diagnostic data in directory=[cdmp_20190324055327], requested by (instance=1, osid=29534 (LGWR)), summary=[abnormal instance termination].

Instance terminated by LGWR, pid = 29534

错误原因：

1、发生ORA-4021 错误的原因

获取library cache lock/pin 超时

2、为什么是 LGWR 终止了db instance

根据 《Bug 18242740 : ACTIVE STANDBY DATABASE CRASHED WITH ORA-4021》整理：

LGWR 需要获取到解析锁（parse lock）才能刷新，可能这个会话话费了大量时间解析。超过了设定时间，依然没有获取到解析锁，就发生了ORA-4021崩溃。

解决办法：

MOS上找到了相同案例的解决方案《LGWR (ospid: Xxx): Terminating The Instance Due To Error 4021 (文档 ID 2177473.1)》，BUG导致ADG宕机。设置隐含参数 _adg_parselock_timeout 可解决该bug，

ALTER SYSTEM set "_adg_parselock_timeout"=550 scope=both;

参考资料

LGWR (ospid: Xxx): Terminating The Instance Due To Error 4021 (文档 ID 2177473.1)

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;

-----------------------------------End By  2019-03-28--------------------------------------------------------