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https://issues.apache.org/jira/browse/HADOOP-3136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12656266#action_12656266
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Matei Zaharia commented on HADOOP-3136:
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I had one comment.. is it possible to change the "findLocalTask" parameter in
JobInProgress.findNewMapTask from a boolean to an int maxLevel for the maximum
level in the topology where you can look? This would be useful for being able
to search for data-local tasks before rack-local tasks. Now data vs rack
locality shouldn't make much of a difference in most workloads, but I had some
tests at Facebook where data-local tasks seemed to be faster, and this is a
small change that will leave this possibility open.
> Assign multiple tasks per TaskTracker heartbeat
> -----------------------------------------------
>
> Key: HADOOP-3136
> URL: https://issues.apache.org/jira/browse/HADOOP-3136
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Devaraj Das
> Assignee: Arun C Murthy
> Fix For: 0.20.0
>
> Attachments: HADOOP-3136_0_20080805.patch,
> HADOOP-3136_1_20080809.patch, HADOOP-3136_2_20080911.patch,
> HADOOP-3136_3_20081211.patch, HADOOP-3136_4_20081212.patch
>
>
> In today's logic of finding a new task, we assign only one task per heartbeat.
> We probably could give the tasktracker multiple tasks subject to the max
> number of free slots it has - for maps we could assign it data local tasks.
> We could probably run some logic to decide what to give it if we run out of
> data local tasks (e.g., tasks from overloaded racks, tasks that have least
> locality, etc.). In addition to maps, if it has reduce slots free, we could
> give it reduce task(s) as well. Again for reduces we could probably run some
> logic to give more tasks to nodes that are closer to nodes running most maps
> (assuming data generated is proportional to the number of maps). For e.g., if
> rack1 has 70% of the input splits, and we know that most maps are data/rack
> local, we try to schedule ~70% of the reducers there.
> Thoughts?
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