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https://issues.apache.org/jira/browse/MAPREDUCE-1800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12869811#action_12869811
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Joydeep Sen Sarma commented on MAPREDUCE-1800:
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how would we detect a slow port/nic? (that currently map-fetch failures at
network level end up catching)
> using map output fetch failures to blacklist nodes is problematic
> -----------------------------------------------------------------
>
> Key: MAPREDUCE-1800
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1800
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Joydeep Sen Sarma
>
> If a mapper and a reducer cannot communicate, then either party could be at
> fault. The current hadoop protocol allows reducers to declare nodes running
> the mapper as being at fault. When sufficient number of reducers do so - then
> the map node can be blacklisted.
> In cases where networking problems cause substantial degradation in
> communication across sets of nodes - then large number of nodes can become
> blacklisted as a result of this protocol. The blacklisting is often wrong
> (reducers on the smaller side of the network partition can collectively cause
> nodes on the larger network partitioned to be blacklisted) and
> counterproductive (rerunning maps puts further load on the (already) maxed
> out network links).
> We should revisit how we can better identify nodes with genuine network
> problems (and what role, if any, map-output fetch failures have in this).
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