[jfoutz]

I think you're overlooking asynchronous writes. Exceptions kind of suck in the asynchronous world, because you need to clean up the write error and you have no idea where you are in your code.

With a getLastError model, you can do your work, then go check for errors when you're really ready.

I'm not saying it's a great api, but it does make sense in context. No idea why the tutorial the op followed didn't talk about the differences, or why asynch is hard.

[untog]

Surely "getLastError" is an extremely questionable concept in the asynchronous world? How do I know the 'last' error is the one relating to the operation my code just executed?

[grey-area]

Presumably this has to be done in the driver directly after the insert call - on the same connection, to ensure that you actually get the last error, and not someone else's error, if you have several instances writing to the db?

[prodigal_erik]

Mongo's wire protocol actually has request IDs, but it appears db.$cmd.findOne({getlasterror:1}) doesn't use that. Instead you have to send it over the same connection as the operation in question, and if you had to reconnect you're just fucked and will never know what you may or may not have committed.