Question

我想从hadoop流媒体作业中的文件中读取一个列表。这是我简单的mapper.py：

#!/usr/bin/env python

import sys
import json

def read_file():
    id_list = []
    #read ids from a file
    f = open('../user_ids','r')
    for line in f:
        line = line.strip()
        id_list.append(line)
    return id_list

if __name__ == '__main__':
    id_list = set(read_file())
    # input comes from STDIN (standard input)
    for line in sys.stdin:
        # remove leading and trailing whitespace
        line = line.strip()
        line = json.loads(line)
        user_id = line['user']['id']
        if str(user_id) in id_list:
            print '%s\t%s' % (user_id, line)

这是我的reducer.py

#!/usr/bin/env python

from operator import itemgetter
import sys

current_id = None
current_list = []
id = None

# input comes from STDIN
for line in sys.stdin:
    # remove leading and trailing whitespace
    line = line.strip()

    # parse the input we got from mapper.py
    id, line = line.split('\t', 1)

    # this IF-switch only works because Hadoop sorts map output
    # by key (here: word) before it is passed to the reducer
    if current_id == id:
        current_list.append(line)
    else:
        if current_id:
            # write result to STDOUT
            print '%s\t%s' % (current_id, current_list)
        current_id = id
        current_list = [line]

# do not forget to output the last word if needed!
if current_id == id:
        print '%s\t%s' % (current_id, current_list)

现在运行它我说：

hadoop jar contrib/streaming/hadoop-streaming-1.1.1.jar -file ./mapper.py \
    -mapper ./mapper.py -file ./reducer.py -reducer ./reducer.py \
    -input test/input.txt  -output test/output -file '../user_ids'

工作开始运行：

13/11/07 05:04:52 INFO streaming.StreamJob:  map 0%  reduce 0%
13/11/07 05:05:21 INFO streaming.StreamJob:  map 100%  reduce 100%
13/11/07 05:05:21 INFO streaming.StreamJob: To kill this job, run:

我收到错误：

job not successful. Error: # of failed Map Tasks exceeded allowed limit. FailedCount: 1.         LastFailedTask: task_201309172143_1390_m_000001
13/11/07 05:05:21 INFO streaming.StreamJob: killJob...

当我没有从文件中读取ID时../user_ids它不会给我任何错误。我认为问题是它无法找到我的../user_id文件。我也使用了hdfs中的位置，仍然无法正常工作。谢谢你的帮助。

Answer 1

hadoop jar contrib/streaming/hadoop-streaming-1.1.1.jar -file ./mapper.py \
  -mapper ./mapper.py -file ./reducer.py -reducer ./reducer.py \
  -input test/input.txt  -output test/output -file '../user_ids'

执行作业时，本地文件路径中是否存在../user_ids？如果确实如此，那么您需要修改映射器代码以解释此文件在运行时在映射器的本地工作目录中可用的事实：

f = open('user_ids','r')

Answer 2

尝试提供文件的完整路径或在执行hadoop命令时确保您位于文件user_ids文件所在的同一目录中

如何使用python在hadoop流媒体作业中使用文件？

2 个答案: