使用dbca建库时遇到ORA-01501: CREATE DATABASE failed这个错误，检查告警日志，发现有下面错误信息：
SMON: enabling tx recovery
Fri Apr 29 14:06:25 HKT 2016
replication_dependency_tracking turned off (no async multimaster replication found)
Starting background process QMNC
Process QMNC died, see its trace file
Fri Apr 29 14:06:26 HKT 2016
Errors in file /u01/app/oracle/admin/EPPS/udump/epps_ora_6832.trc:
ORA-00444: background process "QMNC" failed while starting
ORA-00020: maximum number of processes () exceeded
Fri Apr 29 14:06:26 HKT 2016
Errors in file /u01/app/oracle/admin/EPPS/udump/epps_ora_6832.trc:
ORA-01501: CREATE DATABASE failed
ORA-00450: background process 'QMNC' did not start
ORA-00444: background process "QMNC" failed while starting
ORA-00020: maximum number of processes () exceeded
Error 450 happened during db open, shutting down database
USER: terminating instance due to error 450
Instance terminated by USER, pid = 6832
ORA-1092 signalled during: CREATE DATABASE "EPPS"
从错误信息看，后台进程"QMNC"没有启动，后台进程"QMNC"启动失败，检查对应的跟踪文件，发现ORA-00020: maximum number of processes () exceeded，也就是说因为processes超了，导致后台进程无法启动。
仔细检查后，发现我设置的参数process的值为150，但是在连接模式（Connection Mode）里给了Shared Servrer给了一个很大的值（当时一边操作，一边接电话，把这个值误当成session的值），所以导致后面一系列错误。重新正确设置Shared Servrer值，然后用DBCA建库，问题解决！