meihuak it's a que system. It looks like your database is using a lot of CPU, I'm wondering if it's because you're using Database Ques? I have no idea why your CPU is so high on the database if you're not using that extension.
On your dashboard, what does it say as far as cache and sessions?
For example, Redis works best for large communities since files and sessions take a long time to process. I configure redis from the start before my Flarum goes to the outside world so I don't know what the normal heavy usage is.
Here is Redis: https://discuss.flarum.org/d/37228-friendsofflarum-redis-sessions-cache-queues
Here is DB Qeues: https://discuss.flarum.org/d/28151-database-queue-the-simplest-queue-even-for-shared-hosting
But I don't know if these will solve your issues...
Do you have anything else connected to your databases that may be consuming all those resources?