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I wrote a mapreduce job to extract some info from a dataset. The dataset is users' rating about movies. The number of users is about 250K and the number of movies is about 300k. The output of map is <user, <movie, rating>*> and <movie,<user,rating>*> . In the reducer, I will process these pairs. But when I run the job, the mapper completes as expected, but reducer always complain that Task attempt_* failed to report status for 600 seconds. I know this is due to failed to update status, so I added a call to context.progress() in my code like this: int count = 0; while (values.hasNext()) { if (count++ % 100 == 0) { context.progress(); } /*other code here*/ } Unfortunately, this does not help. Still many reduce tasks failed. Here is the log: Task attempt_201104251139_0295_r_000014_1 failed to report status for 600 seconds. Killing! 11/05/03 10:09:09 INFO mapred.JobClient: Task Id : attempt_201104251139_0295_r_000012_1, Status : FAILED Task attempt_201104251139_0295_r_000012_1 failed to report status for 600 seconds. Killing! 11/05/03 10:09:09 INFO mapred.JobClient: Task Id : attempt_201104251139_0295_r_000006_1, Status : FAILED Task attempt_201104251139_0295_r_000006_1 failed to report status for 600 seconds. Killing! BTW, the error happened in reduce to copy phase, the log says: reduce > copy (28 of 31 at 26.69 MB/s) > :Lost task tracker: tracker_hadoop-56:localhost/127.0.0.1:34385 Thanks for the help.

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