Syntax: fastcgi_send_lowat size; Default: fastcgi_send_lowat 0; Context: http, server, location
If the directive is set to a non-zero value, nginx will try to minimize the number of send operations on outgoing connections to a FastCGI server by using either NOTE_LOWAT flag of the kqueue method, or the SO_SNDLOWAT socket option, with the specified size.
This directive is ignored on Linux, Solaris, and Windows.