need some help with nginx keep_alive setting

Hello,

could somebody give me a clear explanation for these Nginx config

proxy_http_version 1.1;
proxy_set_header Connection "";
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;

i have read the nginx documentation but some details explanation would be very much appreciated. also its not clear i should use them only when im using upstream or not. and if im using unix socket do i need them?

also if im using php, above will go into location php, right?

 location ~ \.php$ {
            proxy_http_version 1.1;
            proxy_set_header Connection "";
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection $connection_upgrade;
        }

thanks in advance.