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Avro >> mail # user >> Hadoop Streaming mangles Python-produced Avro


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Hadoop Streaming mangles Python-produced Avro
I've got a rather simple script that takes Twitter data in JSON and turns
it into an Avro file.

from avro import schema, datafile, io
import json, sys
from types import *

def main():
    if len(sys.argv) < 2:
        print "Usage: cat input.json | python2.7 JSONtoAvro.py output"
        return

    s = schema.parse(open("tweet.avsc").read())
    f = open(sys.argv[1], 'wb')

    writer = datafile.DataFileWriter(f, io.DatumWriter(), s, codec 'deflate')

    failed = 0

    for line in sys.stdin:
        line = line.strip()

    try:
        data = json.loads(line)
    except ValueError as detail:
        continue

    try:
        writer.append(data)
    except io.AvroTypeException as detail:
        print line
        failed += 1

writer.close()

print str(failed) + " failed in schema"

if __name__ == '__main__':
    main()

>From there, I use this to feed a basic Hadoop Streaming script (also in
Python) which just pulls out certain elements of the tweets. However, when
I do this, it appears that the input for the script is mangled JSON.
Usually the JSON fails with some errant \u in the middle of the tweet body
or user-defined description.

The Streaming script is rather basic -- it reads from sys.stdin and
attempts to parse the JSON string using the json package.

Here is the bash script I use to invoke Hadoop Streaming:

jars=/usr/lib/hadoop/lib/avro-1.7.1.cloudera.2.jar,/usr/lib/hive/lib/avro-mapred-1.7.1.cloudera.2.jar

hadoop jar /usr/lib/hadoop-mapreduce/hadoop-streaming.jar \
    -files
$jars,$HOME/sandbox/hadoop/streaming/map/tweetMapper.py,$HOME/sandbox/hadoop/streaming/data/keywords.txt,$HOME/sandbox/hadoop/streaming/data/follow-r3.txt
\
     -libjars $jars \
     -input /user/ahanna/avrotest/avrotest.json.avro \
     -output output \
     -mapper "tweetMapper.py -a" \
     -reducer org.apache.hadoop.mapred.lib.IdentityReducer \
     -inputformat org.apache.avro.mapred.AvroAsTextInputFormat \
     -numReduceTasks 1

I'm starting to think this is a bug with
org.apache.avro.mapred.AvroAsTextInputFormat?

--
Alexander Hanna
PhD Student, Department of Sociology
University of Wisconsin-Madison
http://alex-hanna.com
@alexhanna