今天在切换程序时，oracle报如下错误

java.sql.SQLException: Listener refused the connection with the following error:

ORA-12519, TNS:no appropriate service handler found

查看一下错误信息

[oracle@localhost ~]$ oerr ora 12519
12519, 00000, "TNS:no appropriate service handler found"
// *Cause: The listener could not find any available service handlers that
// are appropriate for the client connection.
// *Action: Run "lsnrctl services" to ensure that the instance(s) have
// registered with the listener, and are accepting connections.

从上面的错误信息可以看出，是由于用户请求时没有可用的连接了。这时才想起程序大概有500个线程同时向数据库插入数据，而建库时默认为300，显然不够用，把连接数设置为800，错误就不存在了。

处理过程：

1. 以DBA身份登录数据库，select count(*) from v$session;查看当前所有连接数，show prameter processes;查看最大连接数
2. 修改processes参数为800，alter system set processes=800 scope=spfile;
3. 重起数据库