= 2010-05-10 =

 * 測試 [http://homepage.mac.com/j.norstad/matrix-multiply/index.html A MapReduce Algorithm for Matrix Multiplication] 所提供之矩陣相乘範例
   * 發現會有 IOException 錯誤訊息，肇因於 /tmp/MatrixMultiply/out/_logs 是目錄而不是檔案
{{{
10/05/10 15:23:23 INFO input.FileInputFormat: Total input paths to process : 1
10/05/10 15:23:23 INFO mapred.JobClient: Running job: job_201005101012_0016
10/05/10 15:23:24 INFO mapred.JobClient:  map 0% reduce 0%
10/05/10 15:23:33 INFO mapred.JobClient:  map 100% reduce 0%
10/05/10 15:23:45 INFO mapred.JobClient:  map 100% reduce 100%
10/05/10 15:23:47 INFO mapred.JobClient: Job complete: job_201005101012_0016
..........
Exception in thread "main" java.io.IOException: Cannot open filename /tmp/MatrixMultiply/out/_logs
        at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.openInfo(DFSClient.java:1497)
}}}
   * [解法] 修改 !TestMatrixMultiply.java，並以單機 !LocalRunner 執行。( hadoop 0.20.2 預設用 !LocalRunner )
{{{
jazz@drbl:~$ wget http://ftp.twaren.net/Unix/Web/apache/hadoop/core/hadoop-0.20.2/hadoop-0.20.2.tar.gz
jazz@drbl:~$ tar zxvf hadoop-0.20.2.tar.gz
jazz@drbl:~$ cd hadoop-0.20.2
jazz@drbl:~/hadoop-0.20.2$ echo "export JAVA_HOME=/usr/lib/jvm/java-6-sun/" >> conf/hadoop-env.sh
jazz@drbl:~/hadoop-0.20.2$ wget http://trac.nchc.org.tw/grid/raw-attachment/wiki/jazz/10-05-10/matrix.tar.gz
jazz@drbl:~/hadoop-0.20.2$ tar zxvf matrix.tar.gz
jazz@drbl:~/hadoop-0.20.2$ cd matrix/
jazz@drbl:~/hadoop-0.20.2/matrix$ ant
jazz@drbl:~/hadoop-0.20.2/matrix$ mv matrix.jar ../.
jazz@drbl:~/hadoop-0.20.2/matrix$ cd ..
jazz@drbl:~/hadoop-0.20.2$ bin/hadoop jar matrix.jar TestMatrixMultiply
}}}