id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
991	http2 uses suboptimal stream prioritization making http/2 slower than http/1.1	vojtech.kurka@…		"When using connection with low bandwidth (G2, GPRS...), our page render starts 60% later with HTTP/2 with HTTP 1.1

The problem is that the main (blocking) CSS file is downloaded in parallel with images on HTTP/2. So the CSS download shares bandwidth with a lot of images that should have much lower priority. Our CSS file is 50KB gzipped and our images in total are much more than 50KB.

HTTP 1.1 doesn't download all images in parallel- it's limited by the total number of TCP connections, so the CSS download finishes much faster and page render can start much sooner.

Ilya Grigorik wrote it could be a problem in nginx http/2 implementation. https://twitter.com/igrigorik/status/737649411325468673

One image is worth thousand words, here it is: https://twitter.com/vojtechkurka/status/736212847982583809

The browser I'm using is Chrome 51 on Mac OS.

We can't use HTTP/2 to production because of this behaviour. It would make mobile user experience much worse than now on HTTP/1.1."	defect	closed	major		other	1.11.x	invalid			Linux mycentosbox 2.6.32-573.18.1.el6.x86_64 #1 SMP Tue Feb 9 22:46:17 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.11.0
built by gcc 4.4.7 20120313 (Red Hat 4.4.7-16) (GCC) 
built with OpenSSL 1.0.2h  3 May 2016
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib64/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp --http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp --http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx --with-http_ssl_module --with-openssl=/opt/lib/openssl-1.0.2h --with-http_realip_module --with-http_addition_module --with-http_sub_module --with-http_dav_module --with-http_flv_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_random_index_module --with-http_secure_link_module --with-http_stub_status_module --with-http_auth_request_module --with-http_xslt_module=dynamic --with-http_image_filter_module=dynamic --with-http_geoip_module=dynamic --with-http_perl_module=dynamic --add-dynamic-module=njs-1c50334fbea6/nginx --with-threads --with-stream --with-stream_ssl_module --with-http_slice_module --with-mail --with-mail_ssl_module --with-file-aio --with-ipv6 --with-http_v2_module --with-cc-opt='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic'"