I've had multiple instances of production data corruption with MongoDB. One of them unrecoverable using normal tools (as in, exporting data or attempting to re

I've had multiple instances of production data corruption with MongoDB. One of them unrecoverable using normal tools (as in, exporting data or attempting to replicate it just outright failed). Luckily that was a non-critical system, but if it hadn't been, it would have been a disaster. Hundreds of gigabytes of documents were unrecoverable, at least by our database folks. The bigger issue I've seen was that some major ORMs were relying on some (apparently undefined?) behavior regarding the positional operator with nested collections of documents, and that behavior changed with a minor version. It's harder to blame MongoDB for that one, but the data corruption was cancerous – it multiplied on every document save.