Hadoop which java

Users should consider the network and CPU overheads of erasure coding when deploying this feature. It should be used only in a test capacity. The Hadoop shell scripts have been rewritten to fix many long-standing bugs and include some new features.

While an eye has been kept towards compatibility, some changes may break existing installations. More details are available in the Unix Shell Guide documentation. Power users will also be pleased by the Unix Shell API documentation, which describes much of the new functionality, particularly related to extensibility. The hadoop-client Maven artifact available in 2. This can be problematic if the versions of these transitive dependencies conflict with the versions used by the application.

A notion of ExecutionType has been introduced, whereby Applications can now request for containers with an execution type of Opportunistic. Containers of this type can be dispatched for execution at an NM even if there are no resources available at the moment of scheduling.

In such a case, these containers will be queued at the NM, waiting for resources to be available for it to start. Opportunistic containers are of lower priority than the default Guaranteed containers and are therefore preempted, if needed, to make room for Guaranteed containers.

This should improve cluster utilization. Opportunistic containers are by default allocated by the central RM, but support has also been added to allow opportunistic containers to be allocated by a distributed scheduler which is implemented as an AMRMProtocol interceptor. Please see documentation for more details. MapReduce has added support for a native implementation of the map output collector.

By replicating edits to a quorum of three JournalNodes, this architecture is able to tolerate the failure of any one node in the system. However, some deployments require higher degrees of fault-tolerance.

This is enabled by this new feature, which allows users to run multiple standby NameNodes. Note that any change to CLI tool output is considered an incompatible change, so between major versions, the CLI output will not change.

Log output is not intended for automated consumption and may change at any time. The web UIs that are exposed by Hadoop are for human consumption only. Scraping the UIs for data is not a supported use.

No effort is made to ensure any kind of compatibility between the data displayed in any of the web UIs across releases. The following policies govern the upgrade characteristics of the various internal state stores:. Hadoop uses two primary forms of configuration files: XML configuration files and logging configuration files.

The XML configuration files contain a set of properties as name-value pairs. The names and meanings of the properties are defined by Hadoop and are guaranteed to be stable across minor releases. A property can only be removed in a major release and only if it has been marked as deprecated for at least a full major release. Most properties have a default value that will be used if the property is not explicitly set in the XML configuration files.

The default property values will not be changed during a maintenance releas. For details about the properties supported by the various Hadoop components, see the component documentation. Downstream projects and users can add their own properties into the XML configuration files for use by their tools and applications.

While Hadoop makes no formal restrictions about defining new properties, a new property that conflicts with a property defined by Hadoop can lead to unexpected and undesirable results. Users are encouraged to avoid using custom configuration property names that conflict with the namespace of Hadoop-defined properties and thus should avoid using any prefixes used by Hadoop, e. The log output produced by Hadoop daemons and CLIs is governed by a set of configuration files. These files control the minimum level of log message that will be output by the various components of Hadoop, as well as where and how those messages are stored.

Between minor releases no changes will be made to the log configuration that reduce, eliminate, or redirect the log messages. Hadoop makes use of a number of other types of configuration files in a variety of formats, such as the JSON resource profiles configuration or the XML fair scheduler configuration.

No incompatible changes will be introduced to the configuration file formats within a minor release. Even between minor releases incompatible configuration file format changes will be avoided if possible. The location and general structure of the Hadoop configuration files, job history information as consumed by the job history server , and logs files generated by Hadoop will be maintained across maintenance releases.

The contents of the Hadoop distribution, e. JAR files, are subject to change at any time and should not be treated as reliable, except for the client artifacts. Client artifacts and their contents will remain compatible within a major release. It is the goal of the Hadoop development community to allow application code to continue to function unchanged across minor releases and, whenever possible, across major releases.

The current list of client artifacts is as follows:. Some Hadoop components receive information through environment variables. Between minor releases the way Hadoop interprets environment variables will not change in an incompatible way.

In other words, the same value placed into the same variable should produce the same result for all Hadoop releases within the same major version. Hadoop relies on a large number of third-party libraries for its operation. As much as possible the Hadoop developer community works to hide these dependencies from downstream developers. Nonetheless Hadoop does expose some of its dependencies, especially prior to Hadoop 3.

No new dependency will be exposed by Hadoop via the client artifacts between major releases. This practice is strongly discouraged. Several have reported success using it on 1. It is the default in 1. Useful tips for discovering and inspecting Sun JVM confuguration flags are in the following blog post: inspecting-hotspot-jvm-options. OpenJDK has been used to qualify Hadoop 2. No problems were noted. Hadoop has been used on JRockit, though not at "production" scale.

Anyone who has information about compatibility of Hadoop 2. An older version of Hadoop 0. IBM Java can be downloaded here.