Since everyone is sharing their opinion and experience with mongodb I think I’ll share mine.
As an appeal to authority I would like to mention that I have relevant vocational qualifications on the subject (more geared towards scalability and operations). Although I don’t believe it really matters - it will to those who assume I don’t understand best practice.
MongoDB itself is not /really/ a valid choice in many scenarios that it was painted as solving. Their only fault is overzealous marketing, it has (in my opinion) very clear pain points that should be avoided, but those painpoints are antithical to why many people used it in the first place.
Most people pick up mongo because it’s painted as being “beginner developer friendly”, I don’t mean new developers, I mean picking it up and running with it, without understanding it, was made to be incredibly easy. But MongoDB itself needs you to understand your data patterns before you start adding shards, so the technology itself depends on you actually sitting down and designing an architecture while understanding that. These goals are at odds with each other.
In MongoDB (as it was when I was using it in full prod 6+ years ago) you -needed- to understand how your data is going to grow and how it will be queried long before you ever created an index. You could not grow after creation. But using it as a plain document store with no searching and heavy sharding on the document ID is the best way to go. And in that scenario it is much better than most competitors.
In nearly every /other/ scenario its a less favourable choice than another technology of some variety.
I would argue the data loss point but I think if that’s not a solved issue it will be, and I’m fairly certain you can configure it to be slower but correct (my memory is bad).
I am not a MongoDB advocate, nor do I hate the technology outright. I strongly dislike how it was marketed as being a panacea.
And for the same reason I avoid PHP, I will attempt to avoid MongoDB.
(As in; it can be done well but the majority of cases will be poorly implemented)