[Joeri]

We just ported a system that kept large amounts of data in postgres jsonb columns over to mongodb. The jsonb column approach worked fine until we scaled it beyond a certain point, and then it was an unending source of performance bottlenecks. The mongodb version is much faster.

In retrospect we should have gone with mongo from the start, but postgres was chosen because in 99% of circumstances it is good enough. It was the wrong decision for the right reasons.

[martinald]

Yep, I agree there are cases where mongodb will perform better. However, many use cases also require joins and the other goodness that relations provide.

So really the use case for mongo etc is 'very high performance requirements' AND 'does not require relations'.

Many projects may be ok with just one of those. But very few require meet both of those constraints.

FWIW I've seen many cases which are sort of the opposite: great performance with mongodb, but then because of the lack of relations for a reporting feature (for example) performance completely plummets due to horrible hacks being done to query the data model that doesn't work with the schema, eventually requiring a rewrite to RDBMS. I would guess that this is much more common.