At the time of writing, Lemmyworld has the second highest number of active users (compared to all lemmy instances)
Also at the time of writing, Lemmyworld has >99% uptime.
By comparison, other lemmy instances with as many users as Lemmyworld keep going down.
What optimizations has Lemmyworld made to their hosting configuration that has made it more resilient than other instances’ hosting configurations?
See also Does Lemmy cache the frontpage by default (read-only)? on !lemmy_support@lemmy.ml
Saying this without any knowledge of lemmy’s backend… Large, high user count databases with (very quickly) growing demand take more power than generally expected. At a certain point, throwing money at the problem is the solution.