Hi!
I found an important problem with the current configuration, that is likely a major factor in the performance loss we see.
I noticed that https://query.wikidata.org/bigdata/ldf is served on HTTPS, and even with HTTP/2. However, the hypermedia controls inside of the message direcs the server to the HTTP version of the URL:
Yes, I noticed that too, filed as: https://phabricator.wikimedia.org/T153897
Unfortunately, we are now in deployment freeze, until January, so it's hard to fix it immediately, as proper fix requires editing some configs and deploying some patches, and it doesn't seem to be production-breaking. But starting January 2 we have deployments again so it'll be fixed.
But, it should not be that big of an issue since Wikimedia servers use HSTS which means no actual http requests are performed in a modern browser). So I don't think it slows things down that much.