I run a wiki hosting service at https://editthis.info https://editthis.info and each wiki that is hosted uses SQLite. This is nice because it is easy to backup

I run a wiki hosting service at https://editthis.info https://editthis.info and each wiki that is hosted uses SQLite. This is nice because it is easy to backup the dbs, everyone has there own separate db, and with over 250k wikis, most of them defunct, they don't really have any overhead other than disk space. They aren't part of one large database that you need to filter all queries through to get the data you want. Also, it makes it so if I want to shard the system, I can just take have of the dbs and move them to another server and it is trivial to do from a sysadmin point of view.