I don't think it should affect performance very much, because GraphX doesn't serialize ShippableVertexPartition in the "fast path" of mapReduceTriplets execution (instead it calls ShippableVertexPartition.shipVertexAttributes and serializes the result). I think it should only get serialized for speculative execution, if you have that enabled.
By the way, here's the fix: https://github.com/apache/spark/pull/1376 Ankur <http://www.ankurdave.com/>
