When MariaDB went into a tailspin, I spent hours trying to understand the InnoDB error that emerged, likely because of corruption in the database. Best guess, some write error to phpservermon table due to cron function that was writing during a restart or crash.
So, trying to fix the error was fruitless and going nowhere. I couldn’t get the SQL engine to start, no matter what the process or changes to mysql.cnf. The event went to the point of MariaDB reinstall.
It was then that I realized that Time Machine might be my friend. Since this is not a high use site, recovering databases would be simple, right?
So, I headed over to /usr/local/var and, thanks to HomeBrew, eureka! Time Machine had dutifully backed up for over three weeks and beyond. Recover the MySQL folder in its entirety and everything back up and running except for one database. Not sure why on the database, but deleted everything in the offending directory and then used Sequel Pro to delete the database from the directory. Then run mysqlcheck -A and all gets OK. Reload WordPress and update to 5.3, upgrade the database and all is good with the world.
I make it sound easy, but this was a few hours work in between things trying to search the internet for solutions for naught — and trying more than a few tinkering options. So, we are updated and living high on the internet hog with Catalina 10.15.2 and Homebrew bubbling along with it.