Error 2020: Got packet bigger than 'max_allowed_packet' bytes when dumping table XXX

Issue

When you request a backup, the task fails  with this error

mysqldump: Error 2020: Got packet bigger than 'max_allowed_packet' bytes when dumping table XXXXX

Resolution

You need to upsize the max_allowed_packet value on your stack. To do this, add (or edit) a file called .my.cnf in the home directory of a web instance of your stack (if it's production, it's either an instance that starts with web- or ded-, and for non-produciton, it's an instance that starts with staging-) and add/update these lines:

[mysqldump]
max_allowed_packet = 512M

Drush

If that still doesn't work with Drush, add this to the end of the sql-dump command:

--extra-dump=--max_allowed_packet=512M

If you still run into difficulties after that, please file a ticket with Acquia Support.