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parallel.cluster.Hadoop

Hadoop cluster for mapreducer, mapreduce and tall arrays

Description

A parallel.cluster.Hadoop object provides access to a cluster for configuring mapreducer, mapreduce, and tall arrays.

Properties

A parallel.cluster.Hadoop object has the following properties.

PropertyDescription
AdditionalPathsFolders to add to MATLAB search path of workers, specified as a character vector, string or string array, or cell array of character vectors
AttachedFilesFiles and folders that are sent to workers during a mapreduce call, specified as a character vector, string or string array, or cell array of character vectors
AutoAttachFilesSpecifies whether automatically attach files
ClusterMatlabRootSpecifies path to MATLAB for workers to use
HadoopConfigurationFileApplication configuration file to be given to Hadoop
HadoopInstallFolderInstallation location of Hadoop on the local machine
HadoopPropertiesMap of name-value property pairs to be given to Hadoop
LicenseNumberLicense number to use with online licensing
RequiresOnlineLicensingSpecify whether cluster uses online licensing
SparkInstallFolderInstallation location of Spark on the local machine
SparkPropertiesMap of name-value property pairs to be given to Spark

When you offload computations to workers, any files that the client needs for computations must also be available on workers. By default, the client attempts to detect and attach these files. To turn off automatic detection, set the AutoAttachFiles property to false. If the software cannot find all the files, or if sending files from client to worker is slow, use one of these options.

  • If the files are in a folder that is not accessible on the workers, set the AttachedFiles property. The cluster copies each file you specify from the client to the workers.

  • If the files are in a folder that is accessible on the workers, you can set the AdditionalPaths property instead. Use the AdditionalPaths property to add paths to the MATLAB® search path for each worker and avoid copying files unnecessarily from the client to the workers.

HadoopProperties allows you to override configuration properties for Hadoop. See the list of properties in the Hadoop® documentation.

The SparkInstallFolder is by default set to the SPARK_HOME environment variable. This is required for tall array evaluation on Hadoop (but not for mapreduce). For a correctly configured cluster, you only need to set the installation folder.

SparkProperties allows you to override configuration properties for Spark. See the list of properties in the Spark® documentation.

Help

For further help, type:

help parallel.cluster.Hadoop

Specify Memory Properties

Spark enabled Hadoop clusters place limits on how much memory is available. You must adjust these limits to support your workflow.

Size of Data to Gather

The amount of data gathered to the client is limited by the Spark properties:

  • spark.driver.memory

  • spark.executor.memory

The amount of data to gather from a single Spark task must fit in these properties. A single Spark task processes one block of data from HDFS, which is 128 MB of data by default. If you gather a tall array containing most of the original data, you must ensure these properties are set to fit.

If these properties are set too small, you see an error like the following.

Error using tall/gather (line 50)
Out of memory; unable to gather a partition of size 300m from Spark.
Adjust the values of the Spark properties spark.driver.memory and 
spark.executor.memory to fit this partition.
The error message also specifies the property settings you need.

Adjust the properties either in the default settings of the cluster or directly in MATLAB. To adjust the properties in MATLAB, add name-value pairs to the SparkProperties property of the cluster. For example:

cluster = parallel.cluster.Hadoop;
cluster.SparkProperties('spark.driver.memory') = '2048m';
cluster.SparkProperties('spark.executor.memory') = '2048m';
mapreducer(cluster);

Specify Working Memory Size for a MATLAB Worker

The amount of working memory for a MATLAB Worker is limited by the Spark property:

  • spark.yarn.executor.memoryOverhead

By default, this is set to 2.5 GB. You typically need to increase this if you use arrayfun, cellfun, or custom datastores to generate large amounts of data in one go. It is advisable to increase this if you come across lost or crashed Spark Executor processes.

You can adjust these properties either in the default settings of the cluster or directly in MATLAB. To adjust the properties in MATLAB, add name-value pairs to the SparkProperties property of the cluster. For example:

cluster = parallel.cluster.Hadoop; 
cluster.SparkProperties('spark.yarn.executor.memoryOverhead') = '4096m';
mapreducer(cluster);

Version History

Introduced in R2014b

See Also

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