// Databricks notebook source exported at Sat, 18 Jun 2016 07:18:41 UTC

Scalable Data Science

prepared by Raazesh Sainudiin and Sivanand Sivaram

supported by and

This is an elaboration of the Apache Spark 1.6 sql-progamming-guide.

Overview

Spark Sql Programming Guide

  • Overview
    • SQL
    • DataFrames
    • Datasets
  • Getting Started
    • Starting Point: SQLContext
    • Creating DataFrames
    • DataFrame Operations
    • Running SQL Queries Programmatically
    • Creating Datasets
    • Interoperating with RDDs
      • Inferring the Schema Using Reflection
      • Programmatically Specifying the Schema
  • Data Sources
    • Generic Load/Save Functions
      • Manually Specifying Options
      • Run SQL on files directly
      • Save Modes
      • Saving to Persistent Tables
    • Parquet Files
      • Loading Data Programmatically
      • Partition Discovery
      • Schema Merging
      • Hive metastore Parquet table conversion
        • Hive/Parquet Schema Reconciliation
        • Metadata Refreshing
      • Configuration
    • JSON Datasets
    • Hive Tables
      • Interacting with Different Versions of Hive Metastore
    • JDBC To Other Databases
    • Troubleshooting
  • Performance Tuning
    • Caching Data In Memory
    • Other Configuration Options
  • Distributed SQL Engine
    • Running the Thrift JDBC/ODBC server
    • Running the Spark SQL CLI

Overview

Spark SQL is a Spark module for structured data processing. Unlike the basic Spark RDD API, the interfaces provided by Spark SQL provide Spark with more information about the structure of both the data and the computation being performed. Internally, Spark SQL uses this extra information to perform extra optimizations. There are several ways to interact with Spark SQL including:

  • SQL,
  • the DataFrames API and
  • the Datasets API.

When computing a result the same execution engine is used, independent of which API/language you are using to express the computation. This unification means that developers can easily switch back and forth between the various APIs based on which provides the most natural way to express a given transformation.

All of the examples on this page use sample data included in the Spark distribution and can be run in the spark-shell, pyspark shell, or sparkR shell.


//This allows easy embedding of publicly available information into any other notebook
//when viewing in git-book just ignore this block - you may have to manually chase the URL in frameIt("URL").
//Example usage:
// displayHTML(frameIt("https://en.wikipedia.org/wiki/Latent_Dirichlet_allocation#Topics_in_LDA",250))
def frameIt( u:String, h:Int ) : String = {
      """<iframe 
 src=""""+ u+""""
 width="95%" height="""" + h + """"
 sandbox>
  <p>
    <a href="http://spark.apache.org/docs/latest/index.html">
      Fallback link for browsers that, unlikely, don't support frames
    </a>
  </p>
</iframe>"""
   }
displayHTML(frameIt("https://en.wikipedia.org/wiki/SQL",500))


displayHTML(frameIt("https://en.wikipedia.org/wiki/Apache_Hive#HiveQL",175))

SQL

One use of Spark SQL is to execute SQL queries written using either a basic SQL syntax or HiveQL. Spark SQL can also be used to read data from an existing Hive installation. For more on how to configure this feature, please refer to the Hive Tables section. When running SQL from within another programming language the results will be returned as a DataFrame. You can also interact with the SQL interface using the command-line or over JDBC/ODBC.

DataFrames

A DataFrame is a distributed collection of data organized into named columns. It is conceptually equivalent to a table in a relational database or a data frame in R/Python, but with richer optimizations under the hood. DataFrames can be constructed from a wide array of sources such as: structured data files, tables in Hive, external databases, or existing RDDs.

The DataFrame API is available in Scala, Java, Python, and R.

Datasets

A Dataset is a new experimental interface added in Spark 1.6 that tries to provide the benefits of RDDs (strong typing, ability to use powerful lambda functions) with the benefits of Spark SQL’s optimized execution engine. A Dataset can be constructed from JVM objects and then manipulated using functional transformations (map, flatMap, filter, etc.).

The unified Dataset API can be used both in Scala and Java. Python does not yet have support for the Dataset API, but due to its dynamic nature many of the benefits are already available (i.e. you can access the field of a row by name naturally row.columnName). Full python support will be added in a future release.

Scalable Data Science

prepared by Raazesh Sainudiin and Sivanand Sivaram

supported by and

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