Hadoop Streaming Python Trivial Example 不工作

Question

我有一个输入文件长这样，已经上传到HDFS /tmp/input（用^A分隔，是非打印字符，这是VI中的视图）

A^A10
A^A7
A^A10
A^A5
A^A10
A^A8
B^A1
A^A9
B^A1
A^A9
B^A1
A^A9
B^A1    
A^A9
B^A1
A^A9
B^A1
A^A9

我写的映射器是这样的：

import sys
for line in sys.stdin:
    name, score = line.strip().split(chr(1))
    print '\t'.join([name, str(int(score)+1)])

reducer 看起来像这样 (similar to)：

import sys
from datetime import datetime

def calc(inputList):
    return min(inputList)

def main():
    current_key = None
    value_list = []
    key = None
    value = None
    result = None
    for line in sys.stdin:
        try:
            line = line.strip()
            key, value = line.split('\t', 1)

            try:
                value = eval(value)
            except:
                continue
            if current_key == key:
                value_list.append(value)
            else:
                if current_key:
                    try:
                        result = str(calc(value_list))
                    except:
                        pass
                    print '%s\t%s' % (current_key, result )
                value_list = [value]
                current_key = key
        except:
        pass
    print '%s\t%s' % (current_key, str(calc(value_list)))

if __name__ == '__main__':
    main()

我在 shell 中测试了 mapper 和 reducer，它对我有用：

$ cat input | python mapper.py | sort -t$'\t' -k1 | python reducer.py 
A   6
B   2

但我未能使用 hadoop 流实现它：

/usr/bin/hadoop 
jar /opt/cloudera/parcels/CDH-4.3.0-1.cdh4.3.0.p0.22/lib/hadoop-0.20-mapreduce/contrib/streaming/hadoop-streaming-2.0.0-mr1-cdh4.3.0.jar 
-file mapper.py 
-mapper mapper.py  
-file reducer.py 
-reducer reducer.py 
-input /tmp/input 
-output /tmp/output

错误输出如下所示：

13/10/07 15:59:02 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
13/10/07 15:59:02 INFO mapred.FileInputFormat: Total input paths to process : 1
13/10/07 15:59:02 INFO streaming.StreamJob: getLocalDirs(): [/tmp/hadoop-a59347/mapred/local]
13/10/07 15:59:02 INFO streaming.StreamJob: Running job: job_201309301959_0089
13/10/07 15:59:02 INFO streaming.StreamJob: To kill this job, run:
13/10/07 15:59:02 INFO streaming.StreamJob: UNDEF/bin/hadoop job  -Dmapred.job.tracker=url1:8021 -kill job_201309301959_0089
13/10/07 15:59:02 INFO streaming.StreamJob: Tracking URL: http://url1:50030/jobdetails.jsp?jobid=job_201309301959_0089
13/10/07 15:59:03 INFO streaming.StreamJob:  map 0%  reduce 0%
13/10/07 15:59:10 INFO streaming.StreamJob:  map 50%  reduce 0%
13/10/07 16:00:10 INFO streaming.StreamJob:  map 100%  reduce 0%
13/10/07 16:00:26 INFO streaming.StreamJob:  map 100%  reduce 1%
13/10/07 16:00:32 INFO streaming.StreamJob:  map 100%  reduce 2%
13/10/07 16:00:37 INFO streaming.StreamJob:  map 100%  reduce 100%
13/10/07 16:00:37 INFO streaming.StreamJob: To kill this job, run:
13/10/07 16:00:37 INFO streaming.StreamJob: UNDEF/bin/hadoop job  -Dmapred.job.tracker=url1:8021 -kill job_201309301959_0089
13/10/07 16:00:37 INFO streaming.StreamJob: Tracking URL: http://url1:50030/jobdetails.jsp?jobid=job_201309301959_0089
13/10/07 16:00:37 ERROR streaming.StreamJob: Job not successful. Error: NA
13/10/07 16:00:37 INFO streaming.StreamJob: killJob...
Streaming Command Failed!

知道我哪里做错了吗？

Answer 1

Hadoop 框架不知道如何运行您的 mapper 和 reducer。有两种可能的修复方法：

修复 1：显式调用 python。

-mapper "python mapper.py" -reducer "python reducer.py"

FIX 2：告诉 Hadoop 在哪里可以找到 Python 解释器。为此，您需要在*.py 文件的第一行明确告诉它在哪里可以找到它。例如：

#!/usr/bin/env python

但是请注意，python 并不总是在 /usr/bin 中（请参阅下面 copumpkin 的评论）。