

Walkthrough of a MongoDB Map/Reduce Job - mdirolf
http://blog.fiesta.cc/post/10980328832/walkthrough-a-mongodb-map-reduce-job

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danielhfrank
Hey Mike, do you think you could talk about how you test those js functions?
Do you actually hardcode them as strings in python, or do you load them from a
separate js file that you can develop / test separately. I've always been a
little sketched out by the requirement that those MR jobs be written in js,
would be curious to hear how you do it.

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mdirolf
That's a great question, and to be honest it's a bit of a pain point so I
probably should've talked about it in the post.

When developing a new M/R job from scratch I start by mirroring (at least part
of) the data to a local database. Then I can iterate locally on the M/R using
print() and printjson() to debug the map() and reduce() functions - those will
print directly to the database log.

I tend to just embed the map() & reduce() functions as Python strings like you
see in the post. I'm confident that there are better ways to handle this,
though. One approach that can be interesting is to do development from the
shell, that way you can write and debug the map() & reduce() in an actual JS
environment. Once you're happy with them you can just drop them in as strings
with the rest of your application code. Would love to hear how other people
are approaching this stuff, too.

All of that said, I expect that the tooling here will improve over time.

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justinhj
That's strange; this site is blocked at my office (we use Brightcloud.com) but
it doesn't seem to have any history of problems.

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dgottlieb
We're using tumblr for our blog if that offers any insight. Otherwise I'm not
sure what could be causing this.

