解决过程：

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

COUNT(*)
----------
       142

SQL> show parameter sessions

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
java_max_sessionspace_size           integer     0
java_soft_sessionspace_limit         integer     0
license_max_sessions                 integer     0
license_sessions_warning             integer     0
logmnr_max_persistent_sessions       integer     1
mts_sessions                         integer     165
sessions                             integer     170
shared_server_sessions               integer     165

SQL> show parameter processes

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
aq_tm_processes                      integer     1
db_writer_processes                  integer     1
job_queue_processes                  integer     10
log_archive_max_processes            integer     2
processes                            integer     150

修改processes和sessions值

SQL> alter system set processes=350 scope=spfile;

System altered

SQL> alter system set sessions=390 scope=spfile;

System altered

SQL>

查看processes和sessions参数，但更改并未生效

重启数据库