A client site came under significant bot traffic.
This large amount of traffic filled up the MySQL tables and my VPS crashed. I discovered the issue was due to WordFence logging each ping and therefore it had created significant DB bloat.
I am not sure if there is an option to turn off logging or curtail it at a certain point in this plugin, but there were several thousand entries in MySQL which lead to a crashed MySQL and consequently to server impairment.
The server logs contained many references as follows
[ERROR] /usr/sbin/mysqld: Table './*****_wrdp1/wp_wfHits' is marked as crashed and should be repaired
I am not sure what is to blame / whether WF or simply due to
I've elected to un-install Wordfence for the time being and replaced with Brute Protect instead (though not the same, it at least is more lightweight protection).