Update: Jan 2020 – newer versions of Dev Desktop, such as the following, are fully 64-bit on macOS:
Version: 2 Built: Sep 18 2019 03:15:11 Control panel rev: a0d1c92 Stack rev: bb3d2d8
It’s worth noting the version of MySQL that comes installed with Acquia Dev Desktop 2 (5.6.41-84.1) is still 32-bit (unlike PHP which is now 64-bit). Recently I was testing with a particularly large database and found it kept crashing with things like:
‘MySQL server has gone away’
Lost connection to MySQL server at ‘reading authorization packet’
Intensive operations such as Drupal-to-Drupal migration tended to trigger this.
I used MySQLTuner but the changes made little difference so then it occurred to me the 32-bit version simply wasn’t up to it, so I installed the latest 64-bit mariadb from homebrew instead and moved the relevant databases over to that (I have mariadb running on port 3306 and Dev Desktop’s MySQL on it’s default 33067).
So far it’s been stable.
See also: Acquia Dev Desktop known issues page