为了解决amazonemr的性能问题，我尝试使用 s3distcp 将文件从s3复制到emr集群进行本地处理。作为第一个测试，我使用 --groupBy 选项将它们折叠成一个（或几个）文件。
作业似乎运行得很好，显示map/reduce进展到100%，但此时进程挂起，再也没有回来。我怎么知道发生了什么事？
源文件是存储在s3中的gzip文本文件，每个文件大约30kb。这是一个普通的amazon emr集群，我正在主节点的shell中运行s3distcp。

hadoop@ip-xxx:~$ hadoop jar /home/hadoop/lib/emr-s3distcp-1.0.jar --src s3n://xxx/click/20140520 --dest hdfs:////data/click/20140520 --groupBy ".*(20140520).*" --outputCodec lzo
14/05/21 20:06:32 INFO s3distcp.S3DistCp: Running with args: [Ljava.lang.String;@26f3bbad
14/05/21 20:06:35 INFO s3distcp.S3DistCp: Using output path 'hdfs:/tmp/9f423c59-ec3a-465e-8632-ae449d45411a/output'
14/05/21 20:06:35 INFO s3distcp.S3DistCp: GET http://169.254.169.254/latest/meta-data/placement/availability-zone result: us-west-2b
14/05/21 20:06:35 INFO s3distcp.S3DistCp: Created AmazonS3Client with conf KeyId AKIAJ5KT6QSV666K6KHA
14/05/21 20:06:37 INFO s3distcp.FileInfoListing: Opening new file: hdfs:/tmp/9f423c59-ec3a-465e-8632-ae449d45411a/files/1
14/05/21 20:06:38 INFO s3distcp.S3DistCp: Created 1 files to copy 2160 files
14/05/21 20:06:38 INFO mapred.JobClient: Default number of map tasks: null
14/05/21 20:06:38 INFO mapred.JobClient: Setting default number of map tasks based on cluster size to : 72
14/05/21 20:06:38 INFO mapred.JobClient: Default number of reduce tasks: 3
14/05/21 20:06:39 INFO security.ShellBasedUnixGroupsMapping: add hadoop to shell userGroupsCache
14/05/21 20:06:39 INFO mapred.JobClient: Setting group to hadoop
14/05/21 20:06:39 INFO mapred.FileInputFormat: Total input paths to process : 1
14/05/21 20:06:39 INFO mapred.JobClient: Running job: job_201405211343_0031
14/05/21 20:06:40 INFO mapred.JobClient:  map 0% reduce 0%
14/05/21 20:06:53 INFO mapred.JobClient:  map 1% reduce 0%
14/05/21 20:06:56 INFO mapred.JobClient:  map 4% reduce 0%
14/05/21 20:06:59 INFO mapred.JobClient:  map 36% reduce 0%
14/05/21 20:07:00 INFO mapred.JobClient:  map 44% reduce 0%
14/05/21 20:07:02 INFO mapred.JobClient:  map 54% reduce 0%
14/05/21 20:07:05 INFO mapred.JobClient:  map 86% reduce 0%
14/05/21 20:07:06 INFO mapred.JobClient:  map 94% reduce 0%
14/05/21 20:07:08 INFO mapred.JobClient:  map 100% reduce 10%
14/05/21 20:07:11 INFO mapred.JobClient:  map 100% reduce 19%
14/05/21 20:07:14 INFO mapred.JobClient:  map 100% reduce 27%
14/05/21 20:07:17 INFO mapred.JobClient:  map 100% reduce 29%
14/05/21 20:07:20 INFO mapred.JobClient:  map 100% reduce 100%
[hangs here]

作业显示为：

hadoop@xxx:~$ hadoop job -list
1 job currently running
JobId   State   StartTime       UserName        Priority        SchedulingInfo
job_201405211343_0031   1       1400702799339   hadoop  NORMAL  NA

目标hdfs目录中没有任何内容：

hadoop@xxx:~$ hadoop dfs -ls /data/click/

有什么想法吗？