???????c)????????a???????????????Spark??????????????HBase??compaction???????????join??sort????????RDD?任??

????Figure 17????local compaction???????????????I/O???????????????????I/O??????????????cache??????????????????????????????????罻??????I/O????????????MapReduce Job??Data Shuffle??????????????????????????I/O?????????????????У(UCSD)??????????о??(MSRA)??????????????????????????????????????I/O?????????о?????????????????SIGCOMM?????????????????????????????·??????????????????г?????????

????Figure 19????combined logging??????????HBase????RS????????DataNode????дlog????????DataNode??????????????RS??log???д??????????/???У??????DataNode????seek???????(????????????I/O?????????I/O)??Combined logging?????????RS??logд??????????У???????DataNode?????I/O??????????I/O??