How to get print output for debugging map/reduce in Mongoid?

Question

I'm writing a map/reduce operation with Mongoid 3.0. I'm trying to use the print statement to debug the JS functions. This is a troubleshooting suggestion from the MongoDB docs, e.g.:

reduce = %Q{
   function(user_id, timestamps) {
      var max = 0;
      timestamps.forEach(function(t) {
        var diff = t.started_at - t.attempted_at;
        if (diff > max) { max = diff; }
      });
      print(user_id + ', ' + max);
      return max;
    };
  }

 MyCollection.all.map_reduce(map, reduce).to_a

Unfortunately the output from the print statement shows up neither on the console nor on the log--it seems that this is suppressed somewhere between the DB, the driver, Moped or any of the intervening layers. Is there a way to turn this on?

Answer 1

It turns out the print statements logs to the MongoDB server log. On OSX, that is /usr/local/var/log/mongodb/mongo.log