How do you manage fragment caching invalidation?

[guillaumebriday]

Hey! 👋

This one’s probably a question for @djmb or @dhh at Basecamp. 😊

I use fragment caching quite a bit, but I often run into issues when the cached content includes helpers, translations (like date formats or text), etc. Here’s an example:

<%# app/views/comments/index.html.erb %>
<%= render partial: 'comments/comment', collection: @comments, cached: true %>

<%# app/views/comments/_comment.html.erb %>
<%= t('comments.title') %>
<%= badge_tag(@comment.status) %>

<%= t(comment.created_at, format: :long) %>

<div class="prose">
  <%= comment.content %>
</div>

If the output of a helper or translation changes, the cache isn’t invalidated unless the associated data (like the comments) is updated.

The Rails docs suggest adding comments to adjust the MD5 hash for cache keys, but that seems really hard to maintain: https://guides.rubyonrails.org/caching_with_rails.html#external-dependencies.

When I used Redis, the cache size was so small that it frequently invalidated itself. But now, with Solid Cache, it doesn’t.

In your video (https://www.youtube.com/watch?v=wYeVne3aRow), you mentioned using a background job to invalidate caches, but I’m unclear on how you handle this process overall.

I guess we could also configure SolidCache with a max_age that matches our deployment frequency, https://github.com/rails/solid_cache?tab=readme-ov-file#configuration, I don't know..

How do you manage this?

[dhh]

Do all such translations using JavaScript. Like the local-time gem does.