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Another small one I'd point out: You can't sort large sets on fields that aren't indexed. It's not just slow, mongo flat out refuses to do it.

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This is actually awesome feature! AppEngine's Datastore requires this as well.

I really wish that PostgreSQL (and other SQL databases) would allow one to enforce such policy, it's a lifesaver.

Agreed. I wish normal SQL dbs would implement a mode where index misses result in errors unless they contain some sort of opt in text.

Some "normal" SQL dbs can, at the very least, be configured to log this. Which is pretty great when you consider some can't.

Mongo servers can be run in a mode that rejects the query with an error if it would result in a row scan. Very useful for safely avoiding bad queries slamming your server.

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