How to perform a word count on text data in HDFS¶
Overview¶
This example counts the number of words in text files that are stored in HDFS.
Who is this for?¶
This how-to is for users of a Spark cluster who wish to run Python code using the YARN resource manager that reads and processes files stored in HDFS.
Spark Wordcount Summary¶
Before you start¶
To execute this example, download the cluster-spark-wordcount.py example script and the cluster-download-wc-data.py script.
For this example, you’ll need Spark running with the YARN resource manager and the Hadoop Distributed File System (HDFS). You can install Spark, YARN, and HDFS using an enterprise Hadoop distribution such as Cloudera CDH or Hortonworks HDP.
You will also need valid Amazon Web Services (AWS) credentials.
Load HDFS data¶
First, we will load the sample text data into the HDFS data store. The following script will transfer sample text data (approximately 6.4 GB) from a public Amazon S3 bucket to the HDFS data store on the cluster.
Download the cluster-download-wc-data.py script to your
cluster and Insert your Amazon AWS credentials in the AWS_KEY and AWS_SECRET variables.
import subprocess
AWS_KEY = ''
AWS_SECRET = ''
s3_path = 's3n://{0}:{1}@blaze-data/enron-email'.format(AWS_KEY, AWS_SECRET)
cmd = ['hadoop', 'distcp', s3_path, 'hdfs:///tmp/enron']
subprocess.call(cmd)
Note: The hadoop distcp command might cause HDFS to fail on smaller instance sizes due to memory limits.
Run the cluster-download-wc-data.py script on the Spark cluster.
python cluster-download-wc-data.py
After a few minutes, the text data will be in the HDFS data store on the cluster and ready for analysis.
Running the Job¶
Download the cluster-spark-wordcount.py example script to
your cluster. This script will read the text files downloaded in step 2 and count all of the words.
# cluster-spark-wordcount.py
from pyspark import SparkConf
from pyspark import SparkContext
HDFS_MASTER = 'HEAD_NODE_IP'
conf = SparkConf()
conf.setMaster('yarn-client')
conf.setAppName('spark-wordcount')
conf.set('spark.executor.instances', 10)
sc = SparkContext(conf=conf)
distFile = sc.textFile('hdfs://{0}:9000/tmp/enron/*/*.txt'.format(HDFS_MASTER))
nonempty_lines = distFile.filter(lambda x: len(x) > 0)
print 'Nonempty lines', nonempty_lines.count()
words = nonempty_lines.flatMap(lambda x: x.split(' '))
wordcounts = words.map(lambda x: (x, 1)) \
.reduceByKey(lambda x, y: x+y) \
.map(lambda x: (x[1], x[0])).sortByKey(False)
print 'Top 100 words:'
print wordcounts.take(100)
Replace the HEAD_NODE_IP text with the IP address of the head node.
Run the script on your Spark cluster using spark-submit The output shows the top 100 words from the sample text data that were returned from the Spark script.
54.237.100.240: Using Spark's default log4j profile: org/apache/spark/log4j-defaults.properties
15/06/13 04:58:42 INFO SparkContext: Running Spark version 1.4.0
[...]
15/06/26 04:32:03 INFO YarnScheduler: Removed TaskSet 7.0, whose tasks have all completed, from pool
15/06/26 04:32:03 INFO DAGScheduler: ResultStage 7 (runJob at PythonRDD.scala:366) finished in 0.210 s
15/06/26 04:32:03 INFO DAGScheduler: Job 3 finished: runJob at PythonRDD.scala:366, took 18.124243 s
[(288283320, ''), (22761900, '\t'), (19583689, 'the'), (13084511, '\t0'), (12330608, '-'),
(11882910, 'to'), (11715692, 'of'), (10822018, '0'), (10251855, 'and'), (6682827, 'in'),
(5463285, 'a'), (5226811, 'or'), (4353317, '/'), (3946632, 'for'), (3695870, 'is'),
(3497341, 'by'), (3481685, 'be'), (2714199, 'that'), (2650159, 'any'), (2444644, 'shall'),
(2414488, 'on'), (2325204, 'with'), (2308456, 'Gas'), (2268827, 'as'), (2265197, 'this'),
(2180110, '$'), (1996779, '\t$0'), (1903157, '12:00:00'), (1823570, 'The'), (1727698, 'not'),
(1626044, 'such'), (1578335, 'at'), (1570484, 'will'), (1509361, 'has'), (1506064, 'Enron'),
(1460737, 'Inc.'), (1453005, 'under'), (1411595, 'are'), (1408357, 'from'), (1334359, 'Data'),
(1315444, 'have'), (1310093, 'Energy'), (1289975, 'Set'), (1281998, 'Technologies,'),
(1280088, '***********'), (1238125, '\t-'), (1176380, 'all'), (1169961, 'other'), (1166151, 'its'),
(1132810, 'an'), (1127730, '&'), (1112331, '>'), (1111663, 'been'), (1098435, 'This'),
(1054291, '0\t0\t0\t0\t'), (1021797, 'States'), (971255, 'you'), (971180, 'which'), (961102, '.'),
(945348, 'I'), (941903, 'it'), (939439, 'provide'), (902312, 'North'), (867218, 'Subject:'),
(851401, 'Party'), (845111, 'America'), (840747, 'Agreement'), (810554, '#N/A\t'), (807259, 'may'),
(800753, 'please'), (798382, 'To'), (771784, '\t$-'), (753774, 'United'), (740472, 'if'),
(739731, '\t0.00'), (723399, 'Power'), (699294, 'To:'), (697798, 'From:'), (672727, 'Date:'),
(661399, 'produced'), (652527, '2001'), (651164, 'format'), (650637, 'Email'), (646922, '3.0'),
(645078, 'licensed'), (644200, 'License'), (642700, 'PST'), (641426, 'cite'), (640441, 'Creative'),
(640089, 'Commons'), (640066, 'NSF'), (639960, 'EML,'), (639949, 'Attribution'),
(639938, 'attribution,'), (639936, 'ZL'), (639936, '(http://www.zlti.com)."'), (639936, '"ZL'),
(639936, 'X-ZLID:'), (639936, '<http://creativecommons.org/licenses/by/3.0/us/>'), (639936, 'X-SDOC:')]
Troubleshooting¶
If something goes wrong consult the FAQ / Known issues page.