##### General

- Overview
- Single Node Setup
- Cluster Setup
- Commands Reference
- FileSystem Shell
- Compatibility Specification
- Downstream Developer's Guide
- Admin Compatibility Guide
- Interface Classification
- FileSystem Specification

##### Common

- CLI Mini Cluster
- Native Libraries
- Proxy User
- Rack Awareness
- Secure Mode
- Service Level Authorization
- HTTP Authentication
- Credential Provider API
- Hadoop KMS
- Tracing
- Unix Shell Guide

##### HDFS

- Architecture
- User Guide
- Commands Reference
- NameNode HA With QJM
- NameNode HA With NFS
- Observer NameNode
- Federation
- ViewFs
- ViewFsOverloadScheme
- Snapshots
- Edits Viewer
- Image Viewer
- Permissions and HDFS
- Quotas and HDFS
- libhdfs (C API)
- WebHDFS (REST API)
- HttpFS
- Short Circuit Local Reads
- Centralized Cache Management
- NFS Gateway
- Rolling Upgrade
- Extended Attributes
- Transparent Encryption
- Multihoming
- Storage Policies
- Memory Storage Support
- Synthetic Load Generator
- Erasure Coding
- Disk Balancer
- Upgrade Domain
- DataNode Admin
- Router Federation
- Provided Storage

##### MapReduce

- Tutorial
- Commands Reference
- Compatibility with 1.x
- Encrypted Shuffle
- Pluggable Shuffle/Sort
- Distributed Cache Deploy
- Support for YARN Shared Cache

##### MapReduce REST APIs

- MR Application Master
- MR History Server

##### YARN

- Architecture
- Commands Reference
- Capacity Scheduler
- Fair Scheduler
- ResourceManager Restart
- ResourceManager HA
- Resource Model
- Node Labels
- Node Attributes
- Web Application Proxy
- Timeline Server
- Timeline Service V.2
- Writing YARN Applications
- YARN Application Security
- NodeManager
- Running Applications in Docker Containers
- Using CGroups
- Secure Containers
- Registry
- Reservation System
- Graceful Decommission
- Opportunistic Containers
- YARN Federation
- Shared Cache
- Using GPU
- Using FPGA
- Placement Constraints
- YARN UI2

##### YARN REST APIs

- Introduction
- Resource Manager
- Node Manager
- Timeline Server
- Timeline Service V.2

##### YARN Service

- Overview
- QuickStart
- Concepts
- Yarn Service API
- Service Discovery
- System Services

##### Submarine

- Index
- QuickStart
- Examples

##### Hadoop Compatible File Systems

- Aliyun OSS
- Amazon S3
- Azure Blob Storage
- Azure Data Lake Storage
- OpenStack Swift

##### Auth

- Overview
- Examples
- Configuration
- Building

##### Tools

- Hadoop Streaming
- Hadoop Archives
- Hadoop Archive Logs
- DistCp
- GridMix
- Rumen
- Resource Estimator Service
- Scheduler Load Simulator
- Hadoop Benchmarking

##### Reference

- Changelog and Release Notes
- Java API docs
- Unix Shell API
- Metrics

##### Configuration

- core-default.xml
- hdfs-default.xml
- hdfs-rbf-default.xml
- mapred-default.xml
- yarn-default.xml
- kms-default.xml
- httpfs-default.xml
- Deprecated Properties

# Apache Hadoop 2.0.2-alpha Release Notes

These release notes cover new developer and user-facing incompatibilities, important issues, features, and major improvements.

- HADOOP-7703 | Major | WebAppContext should also be stopped and cleared

Improved excpetion handling of shutting down web server. (Devaraj K via Eric Yang)

- MAPREDUCE-3348 | Major | mapred job -status fails to give info even if the job is present in History

Fixed a bug in MR client to redirect to JobHistoryServer correctly when RM forgets the app.

- MAPREDUCE-4072 | Major | User set java.library.path seems to overwrite default creating problems native lib loading

-Djava.library.path in mapred.child.java.opts can cause issues with native libraries. LD_LIBRARY_PATH through mapred.child.env should be used instead.

- HDFS-3110 | Major | libhdfs implementation of direct read API

libhdfs is enhanced to read directly into user-supplied buffers when possible, reducing the number of memory copies.

- MAPREDUCE-4017 | Trivial | Add jobname to jobsummary log

The Job Summary log may contain commas in values that are escaped by a ‘\’ character. This was true before, but is more likely to be exposed now.

- MAPREDUCE-3812 | Major | Lower default allocation sizes, fix allocation configurations and document them

Removes two sets of previously available config properties:

1. ( yarn.scheduler.fifo.minimum-allocation-mb and yarn.scheduler.fifo.maximum-allocation-mb ) and,
2. ( yarn.scheduler.capacity.minimum-allocation-mb and yarn.scheduler.capacity.maximum-allocation-mb )

In favor of two new, generically named properties:

1. yarn.scheduler.minimum-allocation-mb - This acts as the floor value of memory resource requests for containers.
2. yarn.scheduler.maximum-allocation-mb - This acts as the ceiling value of memory resource requests for containers.

Both these properties need to be set at the ResourceManager (RM) to take effect, as the RM is where the scheduler resides.

Also changes the default minimum and maximums to 128 MB and 10 GB respectively.

- HDFS-3318 | Blocker | Hftp hangs on transfers >2GB

WARNING: No release note provided for this change.

- HADOOP-8327 | Major | distcpv2 and distcpv1 jars should not coexist

Resolve sporadic distcp issue due to having two DistCp classes (v1 & v2) in the classpath.

- HADOOP-8388 | Minor | Remove unused BlockLocation serialization

WARNING: No release note provided for this change.

- MAPREDUCE-3543 | Critical | Mavenize Gridmix.

Note that to apply this you should first run the script - ./MAPREDUCE-3543v3.sh svn, then apply the patch.

If this is merged to more then trunk, the version inside of hadoop-tools/hadoop-gridmix/pom.xml will need to be udpated accordingly.

- MAPREDUCE-3873 | Minor | Nodemanager is not getting decommisioned if the absolute ip is given in exclude file.

Fixed NodeManagers’ decommissioning at RM to accept IP addresses also.

- HADOOP-8368 | Minor | Use CMake rather than autotools to build native code

WARNING: No release note provided for this change.

- HDFS-3522 | Major | If NN is in safemode, it should throw SafeModeException when getBlockLocations has zero locations

getBlockLocations(), and hence open() for read, will now throw SafeModeException if the NameNode is still in safe mode and there are no replicas reported yet for one of the blocks in the file.

- HADOOP-8458 | Major | Add management hook to AuthenticationHandler to enable delegation token operations support

WARNING: No release note provided for this change.

- HDFS-3518 | Major | Provide API to check HDFS operational state

Add a utility method HdfsUtils.isHealthy(uri) for checking if the given HDFS is healthy.

- MAPREDUCE-4311 | Major | Capacity scheduler.xml does not accept decimal values for capacity and maximum-capacity settings

WARNING: No release note provided for this change.

- HDFS-3475 | Trivial | Make the replication and invalidation rates configurable

This change adds two new configuration parameters.

# {{dfs.namenode.invalidate.work.pct.per.iteration}} for controlling deletion rate of blocks.

# {{dfs.namenode.replication.work.multiplier.per.iteration}} for controlling replication rate. This in turn allows controlling the time it takes for decommissioning.

Please see hdfs-default.xml for detailed description.

- HDFS-3446 | Major | HostsFileReader silently ignores bad includes/excludes

HDFS no longer silently ignores missing or unreadable host files specified by dfs.hosts or dfs.hosts.exclude. In order to specify that no hosts should be included or excluded, administrators should either refrain from setting the relevant config properties, or create an empty file in order to represent an empty list.

- HADOOP-8533 | Major | Remove Parallel Call in IPC

Merged the change to branch-2

- MAPREDUCE-3940 | Major | ContainerTokens should have an expiry interval

ContainerTokens now have an expiry interval so that stale tokens cannot be used for launching containers.

- HDFS-3675 | Minor | libhdfs: follow documented return codes

WARNING: No release note provided for this change.

- HDFS-2617 | Major | Replaced Kerberized SSL for image transfer and fsck with SPNEGO-based solution

Due to the requirement that KSSL use weak encryption types for Kerberos tickets, HTTP authentication to the NameNode will now use SPNEGO by default. This will require users of previous branch-1 releases with security enabled to modify their configurations and create new Kerberos principals in order to use SPNEGO. The old behavior of using KSSL can optionally be enabled by setting the configuration option “hadoop.security.use-weak-http-crypto” to “true”.

- HADOOP-8551 | Major | fs -mkdir creates parent directories without the -p option

FsShell’s “mkdir” no longer implicitly creates all non-existent parent directories. The command adopts the posix compliant behavior of requiring the “-p” flag to auto-create parent directories.

- HDFS-3697 | Minor | Enable fadvise readahead by default

The datanode now performs 4MB readahead by default when reading data from its disks, if the native libraries are present. This has been shown to improve performance in many workloads. The feature may be disabled by setting dfs.datanode.readahead.bytes to “0”.

- HDFS-3755 | Major | Creating an already-open-for-write file with overwrite=true fails

This is an incompatible change: Before this change, if a file is already open for write by one client, and another client calls fs.create() with overwrite=true, an AlreadyBeingCreatedException is thrown. After this change, the file will be deleted and the new file will be created successfully.

- HADOOP-8703 | Major | distcpV2: turn CRC checking off for 0 byte size

distcp skips CRC on 0 byte files.

- HADOOP-8689 | Major | Make trash a server side configuration option

If fs.trash.interval is configured on the server then the client’s value for this configuration is ignored.

- HADOOP-8710 | Major | Remove ability for users to easily run the trash emptier

The trash emptier may no longer be run using “hadoop org.apache.hadoop.fs.Trash”. The trash emptier runs on the NameNode (if configured). Old trash checkpoints may be deleted using “hadoop fs -expunge”.

- HDFS-2727 | Minor | libhdfs should get the default block size from the server

libhdfs now uses the server block size configuration rather than the deprecated dfs.block.size client configuration.

- HDFS-2686 | Major | Remove DistributedUpgrade related code

This jira removes functionality that has not been used/applicable since release 0.17. The incompatibility introduced by this change will not affect any HDFS users.

- HDFS-2793 | Major | Add an admin command to trigger an edit log roll

Introduced a new command, “hdfs dfsadmin -rollEdits” which requests that the active NameNode roll its edit log. This can be useful for administrators manually backing up log segments.

- MAPREDUCE-4629 | Major | Remove JobHistory.DEBUG_MODE

WARNING: No release note provided for this change.

- HADOOP-8794 | Major | Modifiy bin/hadoop to point to HADOOP_YARN_HOME

WARNING: No release note provided for this change.