Using windowing functions in Spark

问题

I am trying to use rowNumber in Spark data frames. My queries are working as expected in Spark shell. But when i write them out in eclipse and compile a jar, i am facing an error

 16/03/23 05:52:43 ERROR ApplicationMaster: User class threw exception:org.apache.spark.sql.AnalysisException: Could not resolve window function 'row_number'. Note that, using window functions currently requires a HiveContext;
org.apache.spark.sql.AnalysisException: Could not resolve window function 'row_number'. Note that, using window functions currently requires a HiveContext;

My queries

import org.apache.spark.sql.functions.{rowNumber, max, broadcast}
import org.apache.spark.sql.expressions.Window
val w = Window.partitionBy($"id").orderBy($"value".desc)

val dfTop = df.withColumn("rn", rowNumber.over(w)).where($"rn" <= 3).drop("rn")

I am not using HiveContext while running the queries in Spark shell. Not sure why it is returning an error when i run the same as a jar file. And also I am running the scripts on Spark 1.6.0 if that helps. Did anyone face similar issue?

回答1:

I have already answered a similar question before. The error message says all. With spark < version 2.x, you'll need a HiveContext in your application jar, no other way around.

You can read further about the difference between SQLContextand HiveContext here.

SparkSQL has a SQLContext and a HiveContext. HiveContext is a super set of the SQLContext. The Spark community suggest using the HiveContext. You can see that when you run spark-shell, which is your interactive driver application, it automatically creates a SparkContext defined as sc and a HiveContext defined as sqlContext. The HiveContext allows you to execute SQL queries as well as Hive commands.

You can try to check that inside of your spark-shell :

Welcome to
      ____              __
     / __/__  ___ _____/ /__
    _\ \/ _ \/ _ `/ __/  '_/
   /___/ .__/\_,_/_/ /_/\_\   version 1.6.0
      /_/

Using Scala version 2.10.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_74)

scala> sqlContext.isInstanceOf[org.apache.spark.sql.hive.HiveContext]
res0: Boolean = true

scala> sqlContext.isInstanceOf[org.apache.spark.sql.SQLContext]
res1: Boolean = true

scala> sqlContext.getClass.getName
res2: String = org.apache.spark.sql.hive.HiveContext

By inheritance, HiveContext is actually an SQLContext, but it's not true the other way around. You can check the source code if you are more intersted in knowing how does HiveContext inherits from SQLContext.

Since spark 2.0, you'll just need to create a SparkSession (as the single entry point) which removes the HiveContext/SQLContext confusion issue.

回答2:

For Spark 2.0, it is recommended to use SparkSession as the single entry point. It eliminates the HiveContext/SqlContext confusion issue.

import org.apache.spark.sql.SparkSession
val session = SparkSession.builder
    .master("local")
    .appName("application name")
    .getOrCreate()

Check out this databricks article for how to use it.

来源：https://stackoverflow.com/questions/36171349/using-windowing-functions-in-spark

标签

apache-spark

apache-spark-sql

window-functions