MariaDB deactivating

Hi, I was trying to find out why my Wordpress website shutdown. Then I saw someone suggest to check MySQL. So I run

sudo service mysql status

and it shows

mariadb.service - MariaDB 10.3.27 database server
   Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
   Active: deactivating (stop-sigterm) (Result: exit-code) since Mon 2021-09-06 15:33:14 CST; 1h 36min ago
     Docs: man:mysqld(8)
           https://mariadb.com/kb/en/library/systemd/
  Process: 29034 ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld (code=exited, status=0/SUCCESS)
  Process: 29035 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status=0/SUCCESS)
  Process: 29037 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] && VAR= ||   VAR=`cd /usr/bin/..; /usr/bin/galer
  Process: 29084 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION (code=exited, status=1/
 Main PID: 29084 (code=exited, status=1/FAILURE)
   Status: "MariaDB server is down"
    Tasks: 3 (limit: 1150)
   Memory: 68.6M
   CGroup: /system.slice/mariadb.service
           └─27388 /usr/sbin/mysqld

Sep 06 16:58:15 server systemd[1]: Starting MariaDB 10.3.27 database server...
Sep 06 16:58:15 server systemd[1]: mariadb.service: Found left-over process 27388 (mysqld) in control group while start
Sep 06 16:58:15 server systemd[1]: This usually indicates unclean termination of a previous run, or service implementat
Sep 06 16:58:15 server mysqld[29084]: 2021-09-06 16:58:15 0 [Note] /usr/sbin/mysqld (mysqld 10.3.27-MariaDB-0+deb10u1) 
Sep 06 16:58:15 server mysqld[29084]: 2021-09-06 16:58:15 0 [Warning] Could not increase number of max_open_files to mo
Sep 06 16:58:48 server systemd[1]: mariadb.service: Main process exited, code=exited, status=1/FAILURE

I also try the
define('WP_ALLOW_REPAIR', true);
It won't work.

I have no idea how should I do next…Please help. Much thanks!