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https://issues.apache.org/jira/browse/HADOOP-4396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12639552#action_12639552
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Devaraj Das commented on HADOOP-4396:
-------------------------------------
Raghu, I pasted a portion of the beginning of the task logs for one of the map
tasks where the problem showed up. Notice the time when the map started running
(15:05:15) and note the time when the first spill happened (15:13:17). The
entire time duration (~8 minutes) was spent in consuming ~128MB of data from
the dfs (and this happened to be a task that got scheduled on a data-local
node). Quite unexpected since in the normal case it takes a few seconds... The
strange thing is that it is not a node issue. So for this run of the sort400, a
couple of maps exhibited this behavior but many ran normally.. And in a
subsequent sort400 run, with the same dataset, *none* of the maps run on this
node exhibited the problem!
2008-10-14 15:05:15,064 INFO org.apache.hadoop.metrics.jvm.JvmMetrics:
Initializing JVM Metrics with processName=MAP, sessionId=
2008-10-14 15:05:15,156 INFO org.apache.hadoop.mapred.MapTask: numReduceTasks:
1741
2008-10-14 15:05:15,173 INFO org.apache.hadoop.mapred.MapTask: io.sort.mb = 128
2008-10-14 15:05:15,378 INFO org.apache.hadoop.mapred.MapTask: data buffer =
102005480/127506848
2008-10-14 15:05:15,379 INFO org.apache.hadoop.mapred.MapTask: record buffer =
335544/419430
2008-10-14 15:05:15,394 INFO org.apache.hadoop.util.NativeCodeLoader: Loaded
the native-hadoop library
2008-10-14 15:05:15,396 INFO org.apache.hadoop.io.compress.LzoCodec:
Successfully loaded & initialized native-lzo library
2008-10-14 15:05:15,591 INFO org.apache.hadoop.io.compress.zlib.ZlibFactory:
Successfully loaded & initialized native-zlib library
2008-10-14 15:05:15,592 INFO org.apache.hadoop.io.compress.CodecPool: Got
brand-new decompressor
2008-10-14 15:05:15,593 INFO org.apache.hadoop.io.compress.CodecPool: Got
brand-new decompressor
2008-10-14 15:05:15,593 INFO org.apache.hadoop.io.compress.CodecPool: Got
brand-new decompressor
2008-10-14 15:05:15,594 INFO org.apache.hadoop.io.compress.CodecPool: Got
brand-new decompressor
2008-10-14 15:13:17,408 INFO org.apache.hadoop.mapred.MapTask: Spilling map
output: buffer full= true
> sort on 400 nodes is now slower than in 18
> ------------------------------------------
>
> Key: HADOOP-4396
> URL: https://issues.apache.org/jira/browse/HADOOP-4396
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.19.0
> Reporter: Jothi Padmanabhan
> Assignee: Jothi Padmanabhan
> Priority: Blocker
> Fix For: 0.19.0
>
>
> Sort on 400 nodes on hadoop release 18 takes about 29 minutes, but with the
> 19 branch takes about 32 minutes. This behavior is consistent.
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