Ora-12519:tns:no appropriate service handler found resolution

Recently done project encountered a connection to Oracle problem, error title: Ora-12519:tns:no Appropriate service handler found, should be the project some algorithms to all the connections are occupied, there is no way to increase the data connection, The following are the specific practices:

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1. select count (*)  from v$process --current number of connections   
2. select value from v$parameter where name =  ' processes '  --database maximum number of connections allowed   
3.   
4. Modify Maximum number of connections:   
5. alter  system set processes = 300 scope = spfile;  
6.   
7. restart database:   
8. shutdown immediate;  
10.   
11. --see which users are currently using data   
12. SELECT  osuser, a.username,cpu_time/executions/1000000| | ' S ',  sql_fulltext,machine   
13. from v$session a, v$sqlarea  b  
14. where a.sql_address =b.address order by cpu_time/ executions desc;  

Ora-12519:tns:no appropriate service handler found resolution