How long can a large Internet company like "Vkontakte" or "Mail.ru" keep backups for a certain number?

Question

Computer networks

How long can a social network like Vkontakte or an e-mail service like Mail.ru keep site backups on their servers for a certain day (for example, January 1, 2015)?

Answer 1

It may never be deleted at all, so as not to reindex the database and not load the servers with deduplication, there is not so much unique content in the total volume, most of the reposts are the same. So large companies simply mark the value as deleted in the database, but physically may not delete it for years.