Thanks for your quickly response.

One more question,

for client_body_buffer_size 16K, if the $request_body >16K, it seems nginx will put the request body into a temp file, and then no logs in log file, even though I enabled the request log. Does that mean the best way to keep the post log is to enable client_body_in_file_only? But the thing is enable client_body_in_file_only will slow down nginx.

So is there any better way to achieve that?