I understand what the fixed name. But I use a mysql sql statement "into outfile" where I store the result of a query with a fixed name. 
The second question is do steps: 
1) is generated in the server example.txt (values 1,2,3,4) in the \ web 
2) Click here to download file-> file is downloaded in the browser 
3) I'll be back to generate example.txt (but with values 1, 2, 3) in the \ web 
4) Click here to download file-> file is downloaded in the browser but with previous values (1,2,3,4). 
The only way to reset it is to restart the webserver 
Agustín