I thought the fact that mongodb data files were essentially mmapped was used as a critique against its durability as a primary database. Is that not true?
Or was that not a relevant critique?
Or was that not a relevant critique?
Databases have different classes of objects (think index vs data, though there are more than just these two), different types of access (e.g. full table scan vs single record select) and a whole lot more complexity than I can cover here. You don't really ever want to page out your indicies, but paging out data is probably fine. You likely want to avoid replacing your entire cache for full table scan of a big table. You probably want to have some concept of ensuring a single user doesn't starve out all your other 1000+ users. Etc etc.
In other words, you can't get away with just opting out of memory management for a database - you need to treat different things differently. I understand that a few years in, the mongo devs eventually caught up to 1990s era mysql and realised this, leading to a new DB engine that was a bit less bad.
From the link of the other comment here, Sqlite disables mmap by default because Linux provides a poor API regarding I/O errors (they are sent as a signal instead)
https://www.mongodb.com/presentations/a-technical-introducti...
I left the place I introduced mongo to, a couple months before they bought WiredTiger