Normally wordpress keeps revision of wp_post table. But for generating a report I need some custom fields to be tracked while any update happens. As custom fields are saved in wp_postmeta table I need to enable the revision for the wp_postmeta table. So how can I enable revision for wp_postmeta table?
I'm sorry, but for now there is no easy way to "enable" revisioning of postmeta. However, you can add post metadata to revisions.
A guy named John Blackburn wrote a pretty good article about adding post metadata to revisions. You find it here: https://johnblackbourn.com/post-meta-revisions-wordpress