Revisions on WP Engine
Every WP Engine site has revisions disabled in its wp-config.php file. When revisions are enabled, our team noticed that performance issues tended to crop up fairly often. Revisions tend to cause database bloat, which in turn causes slow performance. Because of this, it is our recommendation to keep revisions disabled in order to assure optimal site performance. To learn more about database optimization, head to our database best practices guide.
If your site contains existing revisions, please contact our support team via 24/7 live chat your User Portal. It is best to do this prior to migrating or importing your content to avoid a loss of data. Our Support team can help you enable up to 5 revisions for posts. Revisions will be automatically removed after 60 days.
Please note: This is not a retroactive change. It will not add revisions for existing posts automatically, only when you edit them.
Do not add revisions to wp-config.php
The WordPress Codex features a solid article that covers the assorted customizations that one can make on revisions here: http://codex.WordPress.org/Revision_Management. However, please note that changes made to revisions in the wp-config.php file will be overwritten by our system’s scripts. If revisions are required, you must contact Support to enable them. This will ensure the change is permanent, and not overwritten.