Nginx，sendfile和FastCGI

Question

If nginx is only configured to forward requests to a FastCGI backend (Mono, PHP etc), without any file based caching involved, would the use of sendfile on in nginx.conf bring any performance improvements?

Example nginx.conf:

worker_processes  1;
daemon off;

events {
    worker_connections  1024;
    use epoll;
}

http {
    sendfile        on; # <-- ???
    tcp_nopush      on;
    tcp_nodelay     on;

    server {
        listen       80;
        server_name  localhost;

        location / {
            root   /usr/aspnet/;
            fastcgi_pass 127.0.0.1:9000;
            include /etc/nginx/nginx-fastcgi-params.conf;
        }
    }
}

Answer 1

From the Sendfile man pages :

ssize_t sendfile(int out_fd, int in_fd, off_t * offset ", size_t" " count" );
....
The in_fd argument must correspond to a file which supports mmap(2)-like operations (ie, it cannot be a socket).

In other words, enabling sendfile won't make any difference unless nginx is reading from something which can be mapped into the virtual memory space like a file. So it won't make any difference to performance with fastcgi_pass.