What to do if the post has subposts from other user?
My solution: mark the record with a 'deleted' flag, leave all the logical/structural data (user id, post id, etc.) untouched, overwrite/wipe out the post's content, on the webpage display "Post deleted" message. If you want to have an ability to 'unerase' things: mark as deleted, delay the purge.
Cache should be purged as well, though not necessarily in real-time. Backups issue is a complicated one - but is there any use of yearly backups in Facebook case?
My solution: mark the record with a 'deleted' flag, leave all the logical/structural data (user id, post id, etc.) untouched, overwrite/wipe out the post's content, on the webpage display "Post deleted" message. If you want to have an ability to 'unerase' things: mark as deleted, delay the purge.
Cache should be purged as well, though not necessarily in real-time. Backups issue is a complicated one - but is there any use of yearly backups in Facebook case?