我在amazonemr上的mapreduce作业失败了，因为如果第一次尝试未能将结果复制到s3，那么将创建文件（可能是部分文件），随后的reduce尝试将拒绝对已经存在的文件进行写入。
第一次尝试日志：

014-11-30 06:56:19,774 INFO [main] com.amazonaws.latency: StatusCode=[404], Exception=[com.amazonaws.services.s3.model.AmazonS3Exception: Not Found (Service: Amazon S3; Status Code: 404; Error Code: null; Request ID: removed), S3 Extended Request ID: removed=], ServiceName=[Amazon S3], AWSErrorCode=[null], AWSRequestID=[removed], ServiceEndpoint=[https://devel.rui.s3.amazonaws.com], Exception=1, HttpClientPoolLeasedCount=0, RequestCount=1, HttpClientPoolPendingCount=0, HttpClientPoolAvailableCount=0, ClientExecuteTime=[130.087], HttpRequestTime=[118.72], HttpClientReceiveResponseTime=[32.585], RequestSigningTime=[0.646], HttpClientSendRequestTime=[0.835], 
2014-11-30 06:56:19,803 INFO [main] com.amazonaws.latency: StatusCode=[404], Exception=[com.amazonaws.services.s3.model.AmazonS3Exception: Not Found (Service: Amazon S3; Status Code: 404; Error Code: null; Request ID: removed), S3 Extended Request ID: 1removed=], ServiceName=[Amazon S3], AWSErrorCode=[null], AWSRequestID=[removed], ServiceEndpoint=[https://removed.s3.amazonaws.com], Exception=1, HttpClientPoolLeasedCount=0, RequestCount=1, HttpClientPoolPendingCount=0, HttpClientPoolAvailableCount=1, ClientExecuteTime=[27.899], HttpRequestTime=[26.898], HttpClientReceiveResponseTime=[9.405], RequestSigningTime=[0.559], HttpClientSendRequestTime=[1.016], 
2014-11-30 06:56:19,939 INFO [main] com.amazonaws.latency: StatusCode=[200], ServiceName=[Amazon S3], AWSRequestID=[removed], ServiceEndpoint=[https://removedi.s3.amazonaws.com], HttpClientPoolLeasedCount=0, RequestCount=1, HttpClientPoolPendingCount=0, HttpClientPoolAvailableCount=1, ClientExecuteTime=[127.219], HttpRequestTime=[20.791], HttpClientReceiveResponseTime=[15.467], RequestSigningTime=[0.391], ResponseProcessingTime=[82.617], HttpClientSendRequestTime=[0.955], 
2014-11-30 06:56:19,999 INFO [main] org.apache.hadoop.conf.Configuration.deprecation: mapred.skip.on is deprecated. Instead, use mapreduce.job.skiprecords

重试日志（所有日志看起来相同）：

RequestSigningTime=[0.663], ResponseProcessingTime=[12.466], HttpClientSendRequestTime=[0.832], 
2014-11-30 07:23:56,526 WARN [main] org.apache.hadoop.mapred.YarnChild: Exception running child :

java.io.ioexception:文件已存在exists:s3n：//删除/删除/part-r-00005.gz

at com.amazon.ws.emr.hadoop.fs.s3n.S3NativeFileSystem.create(S3NativeFileSystem.java:615)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:910)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:891)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:788)
    at com.amazon.ws.emr.hadoop.fs.EmrFileSystem.create(EmrFileSystem.java:169)
    at org.apache.hadoop.mapreduce.lib.output.TextOutputFormat.getRecordWriter(TextOutputFormat.java:135)
    at org.apache.hadoop.mapred.ReduceTask$NewTrackingRecordWriter.<init>(ReduceTask.java:548)
    at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:622)
    at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:390)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:167)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:415)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1548)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:162)

有趣的是，如果我打开partfiile0005.gz，它里面有东西，是应该的格式。
任何想法，如何解决这个问题（以及如何做到）：a）增加处理延迟（例如，增加超时时间）b）重试删除现有文件（如果已经存在）。