I changed the Acquia Dev Desktop configuration, then when Apache web server and MySQL were restarting MySQL never got back online.
I have enabled the debug option in Acquia Dev Desktop. The logs don't show any clues:
/Applications/DevDesktop/piscript.log
/Applications/DevDesktop/mysql/data/mysql.err
Workaround
I am using the MAMP mysql in the meanwhile, it has this convenient shell script:
/Applications/MAMP/bin/startMysql.sh