Hello Achi,
If  you are not able to log in to Plesk. Then It might be due to your server running out of space.
So, log in to your server and check your disk space.
- df -h
If you have corrected the issue with the excess disk space, you can now try to restart MySQL / MariaDB:
- systemctl restart mysql
If your database server restarts without error, check that you can now access Plesk. If this fails, check the below commands for the most common cause after running out of disk space.
- Where MySQL can’t write the transaction log to disk, It can cause corruption within the log itself. It can prevent MySQL from starting cleanly and requires removing the corrupted log to continue.
- To verify this is the issue, you may see the following error when checking the status:
[root@ws1 ~]# systemctl status mysql.service
     mysql.service - MariaDB 10.1.31 database server
     Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled; vendor preset: disabled)
     Drop-In: /etc/systemd/system/mariadb.service.d
         --migrated-from-my.cnf-settings.conf
   Active: failed (Result: exit-code)
  Status: "MariaDB server is down"
 June 16 08:01:30 ws1.mywebserver.com mysqld[1521]: 2022-06-16  8:01:30 140626098874624 [Note] Recovering after a crash using tc.log
 June 16 08:01:30 ws1.mywebserver.com mysqld[1521]: 2022-06-16  8:01:30 140626098874624 [ERROR] Can't init tc log
For the correction, run the below:
- Access the Server over SSH and move the tc.log of the var/lib/mysql directory.
- [root@ws1 ~] mv /var/lib/mysql/tc.log /root
- After the file has been moved, start MySQL again.
-  systemctl start mysql
- You should then see something similar to the following, with the status as Active:
[root@ws1 ~]# systemctl start mysql
     mysql.service - MariaDB 10.1.31 database server
     Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled; vendor preset: disabled)
     Drop-In: /etc/systemd/system/mariadb.service.d
         --migrated-from-my.cnf-settings.conf
   Active: active (running) (Result: exit-code)
- Ensure the issue is resolved, and try logging in to the Plesk again.