????HDFS????????????洢?????(??????????)????????????????I/O????????????HDFS????HBase?????????????????????????????д??????????????????????????????????????????????????????????????????????????HBase???HDFS???????;??????????????????????????????????д?????HBase?????????????????Java GC??????????????д?????????Facebook Messages(??????FM??)?????????HBase??online storage?????μ?????????(??Apache Hadoop Goes Realtime at Facebook???? SIGMOD 2011)??????????洢???????FAST2014??????????????Analysis of HDFS Under HBase: A Facebook Messages Case Study?????????????????HBase?????????Щ?????????????????HBase??online storage?????????ο????

?????????????????Facebook?????????????tracing/analysis/simulation??FM???????????????????????????????????FM?????????????Щ???????????????????

????FM?????????дI/O????

????Figure 2???????????I/O?????????????FM???????????ж????????????????logging/compaction/replication/caching????д????????

????HBase???????????????????DB?????FS???????????????DB???????????????????????????put()??get()??????????????????????д??HDFS??????ж?д??99/1(Figure 2?е????)??

????????DB?????????????????????????logging??????????Ч?????compaction????????????????????д???????????????????????(overheads)????????д???79/21(Figure 2?е????)??

???????????put()??????HBaseд??????????д????????????д?????Memstore???flush??HFile/HDFS??????????logging???дHLog/HDFS??Memstore?л????????????????дHFile???????????????????дHLog?????append record?????????(HBASE-8155)??????????д?????4???????

????Compaction????????С??HFile?????merge-sorting????HFile????????????HBase????????Compaction????????д?????17?????????????????????????????д??17?Σ?????????????????????????洢??HBase?е?????????????FM???????????????????????????????????а?????????compaction????????????

????HBase??????reliable???HDFS????????HDFS????????????????????????HDFS??д???????????????????local file I/O????????????I/O?????????????????I/O?к?????д??????55/45??

??????????????????????????????????????OS??cache???棬????????????????????cache miss????????????I/O????????????д??????36/64??д??????????