Something like Mastodon is likely 90% reads, or even more. How often is the OP editing their post? When they post, cache it. Kind of like what I did by including it in my original post. Caching is a hard problem because sometimes invalidation results in serious consequences, therefore knowing when to invalidate becomes potentially intractable. In this case there would be few, if any.

it was cache invalidation, and naming things. Just throwing stuff in cache is easy.

Why would it be difficult to cache static text?