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https://issues.apache.org/jira/browse/HADOOP-657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12622464#action_12622464
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Jothi Padmanabhan commented on HADOOP-657:
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The reduce task for sortvalidator , 500 nodes, seem to get stuck with the
following message (several of them), even though the sort itself succeeded
fine. Could there be a bug in the estimation of the reduce input size?
2008-08-14 07:56:16,507 WARN org.apache.hadoop.mapred.JobInProgress: No room
for reduce task. Node tracker_xxx.com:xxx..com/<IPADDR>:58251 has 204889718784
bytes free; but we expect reduce input to take 1004644589190
2008-08-14 07:56:16,508 INFO org.apache.hadoop.mapred.ResourceEstimator:
estimate map will take 150463470 bytes. (blowup = 2*0.04748320346406185)
346406185)
> Free temporary space should be modelled better
> ----------------------------------------------
>
> Key: HADOOP-657
> URL: https://issues.apache.org/jira/browse/HADOOP-657
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Affects Versions: 0.17.0
> Reporter: Owen O'Malley
> Assignee: Ari Rabkin
> Fix For: 0.19.0
>
> Attachments: clean_spaceest.patch, diskspaceest.patch,
> diskspaceest_v2.patch, diskspaceest_v3.patch, diskspaceest_v4.patch,
> spaceest_717.patch
>
>
> Currently, there is a configurable size that must be free for a task tracker
> to accept a new task. However, that isn't a very good model of what the task
> is likely to take. I'd like to propose:
> Map tasks: totalInputSize * conf.getFloat("map.output.growth.factor", 1.0) /
> numMaps
> Reduce tasks: totalInputSize * 2 * conf.getFloat("map.output.growth.factor",
> 1.0) / numReduces
> where totalInputSize is the size of all the maps inputs for the given job.
> To start a new task,
> newTaskAllocation + (sum over running tasks of (1.0 - done) * allocation)
> >=
> free disk * conf.getFloat("mapred.max.scratch.allocation", 0.90);
> So in English, we will model the expected sizes of tasks and only task tasks
> that should leave us a 10% margin. With:
> map.output.growth.factor -- the relative size of the transient data relative
> to the map inputs
> mapred.max.scratch.allocation -- the maximum amount of our disk we want to
> allocate to tasks.
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