Issue Random temporary Database connection error across all Plesk sites

[UnS3eN]

Server operating system version

Almalinux 8.10

Plesk version and microupdate number

18.0.69 #2

For a few weeks now we've been having this weird issue with all sites hosted on Plesk (except the pain one with no database) - all sites would suddenly show a database connections error until I restart mariadb service on Plesk. Even the ones with external DB server. It looks like a mysql.sock issue of some sort but there's nothing in the logs - both system and SQL, - and the service status is not showing anything out of ordinary when that heppens.
It sometime resolves itself ~20 minutes later without my involvement.
I can't figure out where else to look.

 

[Raul A.]

It sounds like all the database service connection slots get used up. By default, you should have 200 connections and 150 connections per user, so that no single user can use up all the connection slots.
Can you run the following when it happens?

plesk db "show full processlist"