Hmm, good question. Usually we redefine them so that we know which exact key we are looking for. If we use JobConf.MAP_MEMORY_MB and the key itself changes from "mapreduce.map.memory.mb" to "something.mapreduce.map.memory.mb", now we end up with different column names in hbase. So redefining them in order to minimize the changes in hadoop which break things for hRaven silently.