init parameter PROCESSES

Initialization parameter PROCESSES defines the max number of user connections that can access the database at a same time. The default value for the parameter is 300.

If the max number exceeds the parameter value, new connection will not be able to connect to the database. Grid Control will report the connection problem and the database will give error in trace file:

ORA-00020: maximum number of processes (300) exceeded

In that case, the issues can be confirmed by number of OS sessions and by database view v$process:

$ echo $ORACLE_SID
$ ps -ef | grep $ORACLE_SID | wc -l
299

SQL> select count(*) from v$process;

COUNT(*)
----------
297

To increase the value, run an alter statement. Then a database bounce is necessary.

SQL> alter system set processes=500 scope=pfile;

I read that below three parameters are related by a formula (in 10G, but might not be always). If database reports ORA-00018 error, you may also consider modifying parameter PROCESSES (or find why the number of sessions jumped).

ORA-00018: maximum number of sessions exceeded

processes=x
sessions=x*1.1+5
transactions=sessions*1.1