webman用nginx做代理之后，在postman上响应需要十几秒，但在浏览器上响应却是毫秒级的？

upstream webman {
    server 127.0.0.1:8787;
    keepalive 10240;
}

server {
  server_name xxx;
  listen 80;
  access_log off;
  root xxx;

  location ^~ / {
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header Host $host;
      proxy_set_header X-Forwarded-Proto $scheme;
      proxy_http_version 1.1;
      proxy_set_header Connection "";
      if (!-f $request_filename){
          proxy_pass http://webman;
      }
  }
}