Hadoop 2.x is developed from hadoop-1.x, with the significant features over hadoop-1.x:
- HDFS HA for NameNode (manual failover)
- NextGen MapReduce (YARN)
- HDFS Federation
- Performance
- Wire-compatibility for both HDFS and YARN/MapReduce (using protobufs)
Hadoop 0.23.x is a trunk which contains:
- HDFS Federation
- NextGen MapReduce (YARN)
Hadoop 1.x is developed from hadoop 0.20-security code support for:
- security
- HBase (append/hsynch/hflush, and security)
- webhdfs (with full support for security)
- performance enhanced access to local files for HBase
- other performance enhancements, bug fixes, and features