What are the limitations of using Accumulators to get a union of a bunch of small sets?
Let's say I have an RDD[Map{String,Any} and i want to do:
rdd.map(accumulator += Set(_.get("entityType").get))
What implication does this have on performance? I'm assuming it's not
immediately aggregating each time I call the += on the Accumulator. Is it
doing a local combine and then occasionally sending the results on the
current partition back to the driver?
