實作三、執行 MapReduce 基本運算
Lab3: Running MapReduce by Examples

Step 0 : rebuild your Hadoop

• download the script of install_hadoop-0.20.2

  ~$ wget http://trac.nchc.org.tw/cloud/raw-attachment/wiki/NCHCCloudCourse100802/install_hadoop_0.20.2
  ~$ chmod a+x install_hadoop_0.20.2
  ~$ ./install_hadoop_0.20.2
  

Sample 1: grep

• grep 這個命令是擷取文件裡面特定的字元，在Hadoop example中此指令可以擷取文件中有此指定文字的字串，並作計數統計
  grep is a command to extract specific characters in documents. In hadoop examples, you can use this command to extract strings match the regular expression and count for matched strings.

$ cd /opt/hadoop
$ bin/hadoop fs -put conf lab3_input
$ bin/hadoop fs -ls lab3_input
$ bin/hadoop jar hadoop-*-examples.jar grep lab3_input lab3_out1 'dfs[a-z.]+' 
 

運作的畫面如下：
You should see procedure like this:

09/03/24 12:33:45 INFO mapred.FileInputFormat: Total input paths to process : 9
09/03/24 12:33:45 INFO mapred.FileInputFormat: Total input paths to process : 9
09/03/24 12:33:45 INFO mapred.JobClient: Running job: job_200903232025_0003
09/03/24 12:33:46 INFO mapred.JobClient:  map 0% reduce 0%
09/03/24 12:33:47 INFO mapred.JobClient:  map 10% reduce 0%
09/03/24 12:33:49 INFO mapred.JobClient:  map 20% reduce 0%
09/03/24 12:33:51 INFO mapred.JobClient:  map 30% reduce 0%
09/03/24 12:33:52 INFO mapred.JobClient:  map 40% reduce 0%
09/03/24 12:33:54 INFO mapred.JobClient:  map 50% reduce 0%
09/03/24 12:33:55 INFO mapred.JobClient:  map 60% reduce 0%
09/03/24 12:33:57 INFO mapred.JobClient:  map 70% reduce 0%
09/03/24 12:33:59 INFO mapred.JobClient:  map 80% reduce 0%
09/03/24 12:34:00 INFO mapred.JobClient:  map 90% reduce 0%
09/03/24 12:34:02 INFO mapred.JobClient:  map 100% reduce 0%
09/03/24 12:34:10 INFO mapred.JobClient:  map 100% reduce 10%
09/03/24 12:34:12 INFO mapred.JobClient:  map 100% reduce 13%
09/03/24 12:34:15 INFO mapred.JobClient:  map 100% reduce 20%
09/03/24 12:34:20 INFO mapred.JobClient:  map 100% reduce 23%
09/03/24 12:34:22 INFO mapred.JobClient: Job complete: job_200903232025_0003
09/03/24 12:34:22 INFO mapred.JobClient: Counters: 16
09/03/24 12:34:22 INFO mapred.JobClient:   File Systems
09/03/24 12:34:22 INFO mapred.JobClient:     HDFS bytes read=48245
09/03/24 12:34:22 INFO mapred.JobClient:     HDFS bytes written=1907
09/03/24 12:34:22 INFO mapred.JobClient:     Local bytes read=1549
09/03/24 12:34:22 INFO mapred.JobClient:     Local bytes written=3584
09/03/24 12:34:22 INFO mapred.JobClient:   Job Counters 
......

• 接著查看結果
  Let's check the computed result of grep from HDFS :

$ bin/hadoop fs -ls lab3_out1
$ bin/hadoop fs -cat lab3_out1/part-00000 

結果如下
You should see results like this:

3	dfs.class
3	dfs.
2	dfs.period
1	dfs.http.address
1	dfs.balance.bandwidth
1	dfs.block.size
1	dfs.blockreport.initial
1	dfs.blockreport.interval
1	dfs.client.block.write.retries
1	dfs.client.buffer.dir
1	dfs.data.dir
1	dfs.datanode.address
1	dfs.datanode.dns.interface
1	dfs.datanode.dns.nameserver
1	dfs.datanode.du.pct
1	dfs.datanode.du.reserved
1	dfs.datanode.handler.count
1	dfs.datanode.http.address
1	dfs.datanode.https.address
1	dfs.datanode.ipc.address
1	dfs.default.chunk.view.size
1	dfs.df.interval
1	dfs.file
1	dfs.heartbeat.interval
1	dfs.hosts
1	dfs.hosts.exclude
1	dfs.https.address
1	dfs.impl
1	dfs.max.objects
1	dfs.name.dir
1	dfs.namenode.decommission.interval
1	dfs.namenode.decommission.interval.
1	dfs.namenode.decommission.nodes.per.interval
1	dfs.namenode.handler.count
1	dfs.namenode.logging.level
1	dfs.permissions
1	dfs.permissions.supergroup
1	dfs.replication
1	dfs.replication.consider
1	dfs.replication.interval
1	dfs.replication.max
1	dfs.replication.min
1	dfs.replication.min.
1	dfs.safemode.extension
1	dfs.safemode.threshold.pct
1	dfs.secondary.http.address
1	dfs.servers
1	dfs.web.ugi
1	dfsmetrics.log

Sample 2 : WordCount

• 如名稱，WordCount會對所有的字作字數統計，並且從a-z作排列
  WordCount example will count each word shown in documents and sorting from a to z.

/opt/hadoop$ bin/hadoop jar hadoop-*-examples.jar wordcount lab3_input lab3_out2

檢查輸出結果的方法同之前方法
Let's check the computed result of wordcount from HDFS :

$ bin/hadoop fs -ls lab3_out2
$ bin/hadoop fs -cat lab3_out2/part-r-00000 

Browsing MapReduce and HDFS via Web GUI

• ​JobTracker Web Interface

• ​NameNode Web Interface

More Examples

可執行的指令一覽表：
Here is a list of hadoop examples :

aggregatewordcount	An Aggregate based map/reduce program that counts the words in the input files.
aggregatewordhist	An Aggregate based map/reduce program that computes the histogram of the words in the input files.
grep	A map/reduce program that counts the matches of a regex in the input.
join	A job that effects a join over sorted, equally partitioned datasets
multifilewc	A job that counts words from several files.
pentomino	A map/reduce tile laying program to find solutions to pentomino problems.
pi	A map/reduce program that estimates Pi using monte-carlo method.
randomtextwriter	A map/reduce program that writes 10GB of random textual data per node.
randomwriter	A map/reduce program that writes 10GB of random data per node.
sleep	A job that sleeps at each map and reduce task.
sort	A map/reduce program that sorts the data written by the random writer.
sudoku	A sudoku solver.
wordcount	A map/reduce program that counts the words in the input files.

You could find more detail at ​org.apache.hadoop.examples