AQ Server EMON Processes Get Error ORA-04021

(Doc ID 1921934.1)

Last updated on OCTOBER 09, 2016

Applies to:

Oracle Database - Enterprise Edition - Version and later
Information in this document applies to any platform.


See errors in database alert log on qxxx processes:

ORA-04021: timeout occurred while waiting to lock object
ORA-00447: fatal error in background process
Emon timeout encountered error 4021

AQ messages may stop being processed.

You have confirmed streams pool size>0.


A systemstate dump may show an EMON slave (Exxx) blocking other sessions waiting for Library Cache lock and not processing.

Example from systemstate:

   OSD pid info: Unix process pid: 79628, image: oracle@rac02db01-dc6 (E003) <<================EMON slave
   Short stack dump:

Current Wait Stack:

     Not in wait; last wait ended 65 min 48 sec ago     <<=====================================NOT IN WAIT
   There are 64 sessions blocked by this session.   <<================================BLOCKING OTHER SESSIONS


NOTE that the emon stack contains kponexpnfy which calls kkcnsli.


A sql trace of the emon slave may also show repeated looping of statement:

select location_name from loc$ where emon# = :1 and connection# = :2






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