Big pipe currently only runs when the user has a session, this is for two reasons:
1. Edge caching doesn't work with streamed responses, at least until Symfony supports HTTP trailers.
2. Big pipe is most useful for dynamic responses with per session (usually per-user)
https://www.drupal.org/project/big_pipe_sessionless → allows for big pipe responses for sessionless users, but has a hard dependency on Drupal's internal page cache.
However a few things have changed recently which may mean we can enable big pipe for sessionless responses too:
📌 Render the navigation toolbar in a placeholder Active means that when placeholders are render-cached, they'll be served directly instead of via big pipe.
📌 Allow the messages block to skip placeholdering Active allows specific placeholders to declare they don't want to be processed by big pipe, and so fall through to the single flush strategy, this is used for the status messages element which is the only placeholder that's shown on every page by default.
With the combination of both of these issues, when render caches are warm for any specific page, big pipe won't be initialised at all for the page - this means no js added, and no streaming. This in turn means those pages would be cacheable as normal in edge caches and the page cache without any special handling (which is what's currently required in big_pipe_sessionless).
If we enable big pipe for sessionless responses, then it will run when render caches are cold. This should mean better perceived performance since the skeleton of the page will be sent faster, and it will be able to take advantage of 🌱 Adopt the Revolt event loop for async task orchestration Active and related issues.
The main disadvantage is that for those pages where big pipe runs, we'll need to disable page caching for those requests - we'd only be able to cache the pages where big pipe doesn't run - usually the second request once page caches are warm. However given a lot of placeholdered content is per-user rather than per-route this should probably still be a high hit rate.
Active
11.0 🔥
big_pipe.module
Explicitly postponing this on 📌 Allow the messages block to skip placeholdering Active but also pushed a start for what I think the minimal changes need to look like.