I have opened a branch for 0.20 (currently 0.20.3 RC2) updated to run on Hadoop 0.21 (currently 0.21-dev) It's passing all unit tests now.
http://svn.apache.org/repos/asf/hadoop/hbase/branches/0.20_on_hadoop-0.21 The aim is for client API compatibility. This is an intermediate step for upgrading to 0.21 so HDFS improvements, e.g. hflush and we hope also HDFS-630, can be incorporated immediately through an upgrade of the deployment but without requiring any change to users of the HBase client API or the Thrift or Stargate connectors. Unlike the 0.20 on Hadoop 0.18.3 branch, the 0.20 on 0.21 branch has a more aggressive strategy for back end changes -- things that touch HDFS and/or a major performance win may go in, evaluated on a case by case basis, as long as they do not change client side API or semantics. For example, the HLog and related THBase improvements from HBase trunk have been backported. I do not expect to maintain this branch beyond some transition period, maybe until 0.21.1. - Andy
