Oracle连接错误：ORA-12519, TNS:no appropriate service handler found

查看oracle允许最大连接数：select value from v$parameter where name = 'processes';
查看当前连接数：select count(*) from v$process;
修改最大连接数：alter system set processes = 500 scope = spfile;
重启oracle：
cmd进入sqlplus：sqlplus / as sysdba
shutdown immediate，等待一会儿，显示数据库关闭
startup，等待数据库开启