Yeah, most of the instances require approval for signups. I started like that, but reading threads about barriers to Lemmy/Fediverse uptake, I tended to agree it's a step that the general public aren't used to, and it's an unnecessary barrier most of the time.

I know (from the Beehaw matrix chat) that they have started rejecting users as they are growing too fast and have an image in mind of what they want their community to be like. Probably if we get lots of new users joining all of a sudden then I'll need to turn on sign-up approvals for a while. That lets us add people at a level we can handle.

From what I've heard, the database CPU usage is the biggest bottleneck for larger instances. I'm actually seeing higher CPU usage now, even though the site says 0 users online. Still less than 50% CPU usage though.

Edit: If I view from the homepage it says 7 users online. Perhaps this is why there's higher CPU usage.

Edit from 3 days later: we've had 30 users online and CPU under 20% so maybe it was higher because of a background job or a bunch of logged out users.