[dude_abides]

To slightly rephrase the OP's question:

  In what use cases does mongo kick postgres's ass?

To the two points you mentioned:

- semi-structured input can be saved as hstore type or as json type;

- and for flexible jobs, you can use pretty much any popular language - PL/R, PL/Python, even PL/C if performance is really critical.

[thibaut_barrere]

I would have replied something similar if that was the question :-) (I use PG a lot these days).

Agreed on the first point (but I'm not sure you get exactly the same type of flexibility in all my use cases - I'll have to make a closer comparison).

For the second point, well not having to handle the schema for ETL jobs is sometimes fairly useful and removes a lot of cruft, that was part of my point (those ETL are code-based, only relying on MongoDB as a flexible store).

[d0ugal]

You can't query JSON easily and hstore is only one level deep. So, no, its not as flexible.

[niels]

You can't query the json type as easily in postgres. I would guess that is an important use case.

[jalada]

I don't know about JSON type but the annoying thing about hstore is everything is a string; there are no types.

[taligent]

Just because you can write an app using assembler doesn't mean it is the best way to do it.

[dude_abides]

Very tempted to ask "In what way does postgres compare to an assembler and mongodb to a high level language?" but I think I'll just assume that you're trolling.

Besides, SQL sounds more high-level than map-reduce to me.