Post revisions lets you tract post changes and revert them back easily but they populates your site _posts table and increases its size. This tutorial contains two simple wp-config.php file hacks you can use for turning off or limiting your posts revisions.
wp-config.php file is locayed in your site’s root directory. Open it for editing and use the following linses of code.
For disabling post revisions add the following line:
define( 'WP_POST_REVISIONS', false);
And use the following line for limiting the post revisions, following line of code limit the post revisions to 3 but you can change this number as per your requirement:
define( 'WP_POST_REVISIONS', 3);