不能连接Oracle数据库了,提示相关的错误

OERR: ORA-12519 TNS:no appropriate service handler found

客户端连接间歇性失败，报错ORA-12519

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. 检查lsnrctl service ，instance已经注册，

状态显示ready时，可以连接。

When the listener believes the current number of connections has reached maximum load,

it may set the state of the service handler for an instance to "blocked" and begin refusing

incoming client connections with either of the following errors: ora-12519 or ora-12516

采用服务动态注册的方式，由PMON 通过SERVICE_UPDATE 来得到目前连接情况，但SERVICE_UPDATE 有时间间隔，

所以，listener显示的连接数和当前实际的连接数可能不同。

查询解决方法:

查看一下数据库现有的进程数，是否已经达到参数processes的大小。

1.select count(*) from v$process; 取得数据库目前的进程数。

2.select value from v$parameter where name = 'processes'; 取得进程数的上限。

3.如已达到上限，修改initSID.ora中的processes的大小。

4.重新启动数据库到nomount状态下，执行create spfile from pfile; 并startup open。

查询数据库自启动以来最大的并发数量

修改最大连接数:

alter system set processes = 300 scope = spfile;

重启数据库:

shutdown immediate;

startup;

--查看当前有哪些用户正在使用数据

SELECT osuser, a.username,cpu_time/executions/1000000||'s', sql_fulltext,machine

from v$session a, v$sqlarea b

where a.sql_address =b.address order by cpu_time/executions desc;