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Hadoop, mail # user - "attempt*" directories in user logs


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"attempt*" directories in user logs
Oleg Zhurakousky 2012-12-09, 14:53
I studying user logs on the two node cluster that I have setup and I was wondering if anyone can shed some light on these "attempt*' directories
>$ ls
attempt_201212051224_0021_m_000000_0  attempt_201212051224_0021_m_000003_0  job-acls.xml
attempt_201212051224_0021_m_000002_0  attempt_201212051224_0021_r_000000_0

I mean its obvious that its talking about 3 attempts for Map task and 1 attempt for reduce task. However my current MR job only results in some output written to "attempt_201212051224_0021_m_000000_0". Nothing is the reduce part (understandably since I don't even have a reducer, so my question is:

1. The two more M attempts. . . what are they?
2. Why was there an attempt to do a Reduce when no reducer was provided.implemented
3. Why my master node only had 1 attempt for M task but the slave had all that's displayed and questioned above (the 'ls' output above is from the slave node)

Thanks
Oleg