How to submit a python wordcount on HDInsight Spark cluster from Jupyter

Question

I am trying to run a python wordcount on a Spark HDInsight cluster and I'm running it from Jupyter. I'm not actually sure if this is the right way to do it, but I couldn't find anything helpful about how to submit a standalone python app on HDInsight Spark cluster.

The code :

import pyspark
import operator
from pyspark import SparkConf
from pyspark import SparkContext
import atexit
from operator import add
conf = SparkConf().setMaster("yarn-client").setAppName("WC")
sc = SparkContext(conf = conf)
atexit.register(lambda: sc.stop())

input = sc.textFile("wasb:///example/data/gutenberg/davinci.txt")
words = input.flatMap(lambda x: x.split())
wordCount = words.map(lambda x: (str(x),1)).reduceByKey(add)

wordCount.saveAsTextFile("wasb:///example/outputspark")

And the error message I get and don't understand :

ValueError                                Traceback (most recent call last)
<ipython-input-2-8a9d4f2cb5e8> in <module>()
      6 from operator import add
      7 import atexit
----> 8 sc = SparkContext('yarn-client')
      9 
     10 input = sc.textFile("wasb:///example/data/gutenberg/davinci.txt")

/usr/hdp/current/spark-client/python/pyspark/context.pyc in __init__(self, master, appName, sparkHome, pyFiles, environment, batchSize, serializer, conf, gateway, jsc, profiler_cls)
    108         """
    109         self._callsite = first_spark_call() or CallSite(None, None, None)
--> 110         SparkContext._ensure_initialized(self, gateway=gateway)
    111         try:
    112             self._do_init(master, appName, sparkHome, pyFiles, environment, batchSize, serializer,

/usr/hdp/current/spark-client/python/pyspark/context.pyc in _ensure_initialized(cls, instance, gateway)
    248                         " created by %s at %s:%s "
    249                         % (currentAppName, currentMaster,
--> 250                             callsite.function, callsite.file, callsite.linenum))
    251                 else:
    252                     SparkContext._active_spark_context = instance

ValueError: Cannot run multiple SparkContexts at once; existing SparkContext(app=pyspark-shell, master=yarn-client) created by __init__ at <ipython-input-1-86beedbc8a46>:7 

Is it actually possible to run python job this way? If yes - it seems to be the problem with SparkContext definition... I tried different ways:

sc = SparkContext('spark://headnodehost:7077', 'pyspark')

and

conf = SparkConf().setMaster("yarn-client").setAppName("WordCount1")
sc = SparkContext(conf = conf)

but no success. What would be the right way to run the job or configure SparkContext?

Answer 1

If you running from Jupyter notebook than Spark context is pre-created for you and it would be incorrect to create a separate context. To resolve the problem just remove the lines that create the context and directly start from:

input = sc.textFile("wasb:///example/data/gutenberg/davinci.txt")

If you need to run standalone program you can run it from command line using pyspark or submit it using REST APIs using Livy server running on the cluster.