A production database of showed 4 cores of CPU burning constantly by 2 process E000 and E001.
On further investigation on Oracle Support we found out it is apparently an unpublished bug which still persists in 11.2.0.4 and 12.1.0.2. You can temporarily solve the issue by killing the OS process for EMON using below method.
$ ps -ef | grep -i e00
oracle 31759 1 0 Jan03 ? 00:00:00 ora_e001_abc1
oracle 31761 1 0 Jan03 ? 00:00:00 ora_e002_abc1
oracle 31763 1 0 Jan03 ? 00:00:00 ora_e003_abc1
oracle 31765 1 0 Jan03 ? 00:00:07 ora_e004_abc1
oracle 32026 1 0 Jan03 ? 00:00:00 ora_e000_abc1
$ kill -9 31759 31761 31763 31765 32026
To solve the issue permanently if release is pre- 11.2.0.3 apply Patch 9735536. To solve the issue permanently from 11.2.0.4 onwards do the below workaround.
connect / as sysdba
alter system set “_client_enable_auto_unregister”=true scope=spfile
shutdown immediate
startup
