We should implement limits on shuffle connections to TaskTracker per job
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Key: MAPREDUCE-2168
URL: https://issues.apache.org/jira/browse/MAPREDUCE-2168
Project: Hadoop Map/Reduce
Issue Type: Improvement
Reporter: Liyin Liang
As trailing map tasks will be attacked by all reduces simultaneously, all the
worker threads that for the http server of a TaskTracker may be occupied by
one job's reduce tasks to fetch map outputs. Then this tasktracker's iowait and
load will be very high (100+ in our cluster, we set tasktracker.http.threads
with 100). What's more, other job's reduces have to wait some time (may be
several minutes) to connect to the TaskTracker to fetch there map's outputs.
So I think we should implement limits on shuffle connections:
1. limit the worker threads' number maybe percent occupied the same job's
reduces ;
2. limit the worker threads' number serving the same map output simultaneously.
Thoughts?
ps: we are using hadoop 0.19.
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