Out of curiosity, did you guys consider running SQL on MongoDB using Postgres foreign tables? What were the pros and cons of that approach for your use-cases?
(In full disclosure, I wrote mongo_fdw for PostgreSQL.)
(In full disclosure, I wrote mongo_fdw for PostgreSQL.)
Our experience was that mongo_fdw doesn't (yet?) give postgres enough information and knobs to plan JOINs efficiently, which is one of the things we wanted. I got a decent amount of leverage out of using mongo_fdw and then cloning to native tables using SELECT INTO, though :)
I'm sure there are other factors involved for MoSQL, but they are probably outside the scope of this post. I'd love chat about them offline.