Apache Spark Bitesize: What is RDD

As the title suggests, this is meant to be a quick post clarifying the core abstraction in Apache Spark: RDD, also known as Resilient Distributed Dataset. RDD is the fundamental data structure in Spark and it is an immutable distributed collections of elements. In simple terms, it is essentially the way Spark represents a set of data, which spreads across multiple machines. As per the formal definition:

RDDs are fault-tolerant, parallel data structures that let users explicitly persist intermediate results in memory, control their partitioning to optimize data placement, and manipulate them using a rich set of operators.

It is possible to create RDDs in two different ways: 1) by calling the parallelise method of the JavaSparkContext class in the driver program; 2) by referencing the dataset which resides on an external storage system.

Here is an example of how to create a parallelised collection via the Scala API:

val myCollection = List(1,3,6,8,9)
val myDistributedCollection = sc.parallelize(myCollection)

This, instead, is an example of how to reference external datasets (Scala API):

val distFile = sc.textFile("myFile.csv")

In the next Apache Spark Bitesize, I will be covering RDD operations: transformations and actions.

Further resources:

  • M. Zaharia et. al. Resilient Distributed Datasets: A Fault-Tolerant Abstraction for In-Memory Cluster Computing, 2001. Available at:  https://people.eecs.berkeley.edu/~matei/papers/2012/nsdi_spark.pdf
  • Apache Spark – Quick Start: http://spark.apache.org/docs/latest/quick-start.html
  • SparkHub: https://sparkhub.databricks.com/

 

 

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Alternative way to install Apache Jena in Eclipse…with a but!

Being a long-term Semantic Web aficionado, I have used Apache Jena with Eclipse several times for manipulating and parsing RDF models and originally installed it by downloading the Windows-compatible distro from http://jena.apache.org/download/index.cgi and and import the libs into my Eclipse project. I have recently found an Eclipse Library Plugin for Jena 2.0  and I was rather excited to be able to work with Jena  without fetching the latest Jena distro and adding it to your Build Path, but the excitement did not last long….The plugin is unfortunately for Jena 2.0 and it does not seem to be compatible with most recent Eclipse versions (e.g. Mars 4.5). Oh well, back to the known route, then!:)

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