Common
Authentication improvements when using an HTTP proxy server. This is useful when accessing WebHDFS via a proxy server.
A new Hadoop metrics sink that allows writing directly to Graphite.
Specification work related to the Hadoop Compatible Filesystem (HCFS) effort.
HDFS
Support for POSIX-style filesystem extended attributes. See the user documentation for more details.
Using the OfflineImageViewer, clients can now browse an fsimage via the WebHDFS API.
The NFS gateway received a number of supportability improvements and bug fixes. The Hadoop portmapper is no longer required to run the gateway, and the gateway is now able to reject connections from unprivileged ports.
The SecondaryNameNode, JournalNode, and DataNode web UIs have been modernized with HTML5 and Javascript.
YARN
YARN's REST APIs now support write/modify operations. Users can submit and kill applications through REST APIs.
The timeline store in YARN, used for storing generic and application-specific information for applications, supports authentication through Kerberos.
The Fair Scheduler supports dynamic hierarchical user queues, user queues are created dynamically at runtime under any specified parent-queue.