Reduce tasks get stuck because of over-estimated task size (regression from
0.18)
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Key: HADOOP-5241
URL: https://issues.apache.org/jira/browse/HADOOP-5241
Project: Hadoop Core
Issue Type: Bug
Components: mapred
Affects Versions: 0.19.0
Environment: Red Hat Enterprise Linux Server release 5.2
JDK 1.6.0_11
Hadoop 0.19.0
Reporter: Andy Pavlo
Priority: Blocker
I have a simple MR benchmark job that computes PageRank on about 600 GB of HTML
files using a 100 node cluster. For some reason, my reduce tasks get caught in
a pending state. The JobTracker's log gets filled with the following messages:
2009-02-12 15:47:29,839 WARN org.apache.hadoop.mapred.JobInProgress: No room
for reduce task. Node tracker_d-59.cs.wisc.edu:localhost/127.0.0.1:33227 has
110125027328 bytes free; but we expect reduce input to take 399642198235
2009-02-12 15:47:29,852 WARN org.apache.hadoop.mapred.JobInProgress: No room
for reduce task. Node tracker_d-67.cs.wisc.edu:localhost/127.0.0.1:48626 has
107537776640 bytes free; but we expect reduce input to take 399642198235
2009-02-12 15:47:29,885 WARN org.apache.hadoop.mapred.JobInProgress: No room
for reduce task. Node tracker_d-73.cs.wisc.edu:localhost/127.0.0.1:58849 has
113631690752 bytes free; but we expect reduce input to take 399642198235
<SNIP>
The weird thing is that I get through about 70 reduce tasks completing before
it hangs. If I reduce the amount of the input data on 100 nodes down to 200GB,
then it seems to work. As I scale the amount of input to the number of nodes, I
can get it work some of the times on 50 nodes and without any problems on 25
nodes and less.
Note that it worked without any problems on Hadoop 0.18 late last year without
changing any of the input data or the actual MR code.
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