Nginx & FastCGI Buffering

I want to ask few questions regarding nginx and fastcgi buffering that i can't find an answer for. 1) Is the fastcgi_buffering values / request or for entire nginx? 2) Assuming that i want to have exactly buffer size of 3MB, what should i do? 3) Assuming that we set the buffer size 3 MB, and we have a file with 10MB in size to send with php what nginx will do? It will buffer the first 3MB, sends them to client, then re-buff the next 3MB etc? Or it will continuously buffer 3MB until we send our whole file? (nginx buffers 3MB, clients get for example 100kb, then nginx will fill the buffer to 3MB again?) 4) Assuming that i set the > fastcgi_max_temp_file_size 0; Nginx will only use Memory to buffer the response? Is a good technique to avoid too much I/O in case we have many requests? 5) Does it makes sense to use fastcgi buffering in endless requests? (eg. sending live stream data with php)