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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4752) Reduce MR AM memory usage through String Interning
Date Fri, 26 Oct 2012 14:49:11 GMT
Robert Joseph Evans created MAPREDUCE-4752:
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             Summary: Reduce MR AM memory usage through String Interning
                 Key: MAPREDUCE-4752
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4752
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: mrv2
            Reporter: Robert Joseph Evans
            Assignee: Robert Joseph Evans


There are a lot of strings that are duplicates of one another in the AM.  This comes from
all of the PB events the come across the wire and also tasks heart-beating in through the
umbilical.  There are even several duplicates from Configuration.  By "interning" all of these
strings on the Heap I have been able to reduce the resting memory usage of the AM to be about
5KB per task attempt.  With about half of this coming from counters.  This results in a 5MB
heap for a typical 1000 task job, or a 500MB heap for a 100,000 task attempt job.  I think
I could cut the size of the counters in half by completely rewriting how counters work in
the AM and History Server, but I don't think it is worth it at this point.

I am still investigating what the memory usage of the AM is like when running very large jobs,
and I will probably have a follow-up JIRA for reducing that memory usage as well.


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