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The Pentaho MapReduce job entry allows you to build MapReduce jobs using Kettle transformations as the Mapper, Combiner, and/or Reducer.

Architecture Overview

TODO

Distributed Cache

Pentaho MapReduce relies on Hadoop's Distributed Cache to distribute the Kettle environment, configuration, and plugins across the cluster. By leveraging the Distributed Cache network traffic is reduced up for subsequent executions as the Kettle environment is automatically configured on each node. This also allows you to use multiple version of Kettle against a single cluster.

How it works

Hadoop's Distributed Cache is a mechanism to distribute files into the working directory of each map and reduce task. The origin of these files is HDFS. Pentaho MapReduce will automatically configure the job to use a Kettle environment from HDFS (configured via pmr.kettle.installation.id, see #ConfigurationOptions). If the desired Kettle environment does not exist, Pentaho MapReduce will take care of "installing" it in HDFS before executing the job.

The default Kettle environment installation path within HDFS is /opt/pentaho/mapreduce/$id, where $id is generally the version of Kettle the environment contains but can easily be a custom build that is tailored for a specific set of jobs.

Configuration options

Pentaho MapReduce can be configured through the pentaho-mapreduce.properties found in the plugin's base directory, or overridden per Pentaho MapReduce job entry if they are defined in the User Defined properties tab.

The currently supported configuration properties are:

Property Name

Description

pmr.kettle.installation.id

Version of Kettle to use from the Kettle HDFS installation directory. If not set we will use the version of Kettle that is used to submit the Pentaho MapReduce job.

pmr.kettle.dfs.install.dir

Installation path in HDFS for the Kettle environment used to execute a Pentaho MapReduce job. This can be a relative path, anchored to the user's home directory, or an absolute path if it starts with a /.

pmr.libraries.archive.file

Pentaho MapReduce Kettle environment runtime archive to be preloaded into kettle.hdfs.install.dir/pmr.kettle.installation.id

pmr.kettle.additional.plugins

Comma-separated list of additional plugins (by directory name) to be installed with the Kettle environment.
e.g. "steps/DummyPlugin,my-custom-plugin"

Customizing the Kettle Environment used by Pentaho MapReduce

TODO

  1. Unzip pentaho-mapreduce-libraries.zip, it contains a single lib/ directory with the required Kettle dependencies
  2. Copy additional libraries to the lib/ directory
  3. Zip up the lib/ directory into pentaho-mapreduce-libraries-custom.zip so the archive contains the lib/ with all jars within it (you may create subdirectories within lib/. All jars found in lib/ and its subdirectories will be added to the classpath of the executing job.)
  4. Update pentaho-mapreduce.properties and update the following properties: 
    pmr.kettle.installation.id=custom
pmr.libraries.archive.file=pentaho-mapreduce-libraries-custom.zip

The next time you execute Pentaho MapReduce the custom Kettle environment will be copied into HDFS at pmr.kettle.dfs.install.dir/custom and used when executing the job. You can switch between Kettle environments by specifying the pmr.kettle.installation.id property as a User Defined property per Pentaho MapReduce job entry or globally in the pentaho-mapreduce.properties file*.

*Note: If the installation referenced by pmr.kettle.installation.id does not exist the archive file and additional plugins currently configured will be used to "install" it into HDFS.

Upgrading from the Pentaho Hadoop Distribution (PHD)

The PHD is no longer required and can be safely removed. If you have modified your Pentaho Hadoop Distribution installation you may wish to preserve these files so that the new Distributed Cache mechanism can take advantage of them. To do so follow the instructions above: Customizing the Kettle Environment used by Pentaho MapReduce.

If you're using a version of the Pentaho Hadoop Distribution (PHD) that allows you to configure the installation directory via mapred-site.xml, perform the following on all TaskTracker nodes:

  1. Remove the pentaho.* properties from your mapred-site.xml
  2. Remove the directories those properties referenced
  3. Restart the TaskTracker process

Appendix A: pentaho-mapreduce-libraries.zip structure:

pentaho-mapreduce-libraries.zip/
  `- lib/
      +- kettle-core-{version}.jar
      +- kettle-engine-{version}.jar
      `- .. (all other required Kettle dependencies)

Appendix B: Example Kettle environment installation directory structure within DFS

/opt/pentaho/mapreduce/
  +- 4.3.0/
  |   +- lib/
  |   |   +- kettle-core-{version}.jar
  |   |   +- kettle-engine-{version}.jar
  |   |   `- .. (all other required Kettle dependencies)
  |   `- plugins/
  |       +- pentaho-big-data-plugin/
  |       `- .. (additional optional plugins)
  `- custom/
      +- lib/
      |   +- kettle-core-{version}.jar
      |   +- kettle-engine-{version}.jar
      |   +- my-custom-code.jar
      |   `- .. (additional optional plugins)
      `- plugins/
          +- pentaho-big-data-plugin/
          |   ..
          `- my-custom-plugin/
              ..
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