时间：2020-12-11 20:55:41 | 栏目：Linux | 点击：次
Hadoop streaming
Hadoop为MapReduce提供了不同的API，可以方便我们使用不同的编程语言来使用MapReduce框架，而不是只局限于Java。这里要介绍的就是Hadoop streaming API。Hadoop streaming 使用Unix的standard streams作为我们mapreduce程序和MapReduce框架之间的接口。所以你可以用任何语言来编写MapReduce程序，只要该语言可以往standard input/output上进行读写。
streamming是天然适用于文字处理的（text processing），当然，也仅适用纯文本的处理，对于需要对象和序列化的场景，hadoop streaming无能为力。它力图使我们能够快捷的通过各种脚本语言，快速的处理大量的文本文件。以下是steaming的一些特点：
常用的Streaming编程语言：
Ruby
下面是一个Ruby编写的MapReduce程序的示例：
map
max_temperature_map.rb：
ruby
#!/usr/bin/env ruby
STDIN.each_line do |line|
val = line
year, temp, q = val[15,4], val[87,5], val[92,1]
puts "#{year}\t#{temp}" if (temp != "+9999" && q =~ /[01459]/)
end
reduce
max_temperature_reduce.rb：
ruby
#!/usr/bin/env ruby
last_key, max_val = nil, -1000000
STDIN.each_line do |line|
key, val = line.split("\t")
if last_key && last_key != key
puts "#{last_key}\t#{max_val}"
last_key, max_val = key, val.to_i
else
last_key, max_val = key, [max_val, val.to_i].max
end
end
puts "#{last_key}\t#{max_val}" if last_key
运行
% hadoop jar $HADOOP_INSTALL/contrib/streaming/hadoop-*-streaming.jar \ -input input/ncdc/sample.txt \ -output output \ -mapper ch02/src/main/ruby/max_temperature_map.rb \ -reducer ch02/src/main/ruby/max_temperature_reduce.rb
Python
Map
#!/usr/bin/env python
import re
import sys
for line in sys.stdin:
val = line.strip()
(year, temp, q) = (val[15:19], val[87:92], val[92:93])
if (temp != "+9999" and re.match("[01459]", q)):
print "%s\t%s" % (year, temp)
Reduce
#!/usr/bin/env python
import sys
(last_key, max_val) = (None, -sys.maxint)
for line in sys.stdin:
(key, val) = line.strip().split("\t")
if last_key and last_key != key:
print "%s\t%s" % (last_key, max_val)
(last_key, max_val) = (key, int(val))
else:
(last_key, max_val) = (key, max(max_val, int(val)))
if last_key:
print "%s\t%s" % (last_key, max_val)
运行
% hadoop jar $HADOOP_INSTALL/contrib/streaming/hadoop-*-streaming.jar \ -input input/ncdc/sample.txt \ -output output \ -mapper ch02/src/main/ruby/max_temperature_map.py\ -reducer ch02/src/main/ruby/max_temperature_reduce.py
Bash shell
Map
#!/usr/bin/env bash # NLineInputFormat gives a single line: key is offset, value is S3 URI read offset s3file # Retrieve file from S3 to local disk echo "reporter:status:Retrieving $s3file" >&2 $HADOOP_INSTALL/bin/hadoop fs -get $s3file . # Un-bzip and un-tar the local file target=`basename $s3file .tar.bz2` mkdir -p $target echo "reporter:status:Un-tarring $s3file to $target" >&2 tar jxf `basename $s3file` -C $target # Un-gzip each station file and concat into one file echo "reporter:status:Un-gzipping $target" >&2 for file in $target/*/* do gunzip -c $file >> $target.all echo "reporter:status:Processed $file" >&2 done # Put gzipped version into HDFS echo "reporter:status:Gzipping $target and putting in HDFS" >&2 gzip -c $target.all | $HADOOP_INSTALL/bin/hadoop fs -put - gz/$target.gz
运行
% hadoop jar $HADOOP_INSTALL/contrib/streaming/hadoop-*-streaming.jar \ -D mapred.reduce.tasks=0 \ -D mapred.map.tasks.speculative.execution=false \ -D mapred.task.timeout=12000000 \ -input ncdc_files.txt \ -inputformat org.apache.hadoop.mapred.lib.NLineInputFormat \ -output output \ -mapper load_ncdc_map.sh \ -file load_ncdc_map.sh
Combiner
在streaming模式下，仍然可以运行Combiner，两种方法：
这里具体解释第二种方法：
% hadoop jar $HADOOP_INSTALL/contrib/streaming/hadoop-*-streaming.jar \ -input input/ncdc/all \ -output output \ -mapper "ch02/src/main/ruby/max_temperature_map.rb | sort | ch02/src/main/ruby/max_temperature_reduce.rb" \ -reducer ch02/src/main/ruby/max_temperature_reduce.rb \ -file ch02/src/main/ruby/max_temperature_map.rb \ -file ch02/src/main/ruby/max_temperature_reduce.rb
注意看-mapper这一行，通关管道的方式，把mapper的临时输出文件（intermediate file，Map完成后的临时文件）作为输入，送到sort进行排序，然后送到reduce脚本，来完成类似于combiner的工作。这时候的输出才真正的作为shuffle的输入，被分组并在网络上发送到Reduce
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