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From Ken Williams <>
Subject Heap Size question.
Date Wed, 01 Jun 2011 11:35:17 GMT

  Hi All,

  I'm a bit confused about the values displayed on the 'jobtracker.jsp' page.
  In particular, there's a section called 'Cluster Summary'.

  I'm running a small 4-machine Hadoop cluster, and when I point a web-browser 
  at my master machine (http://master:50030/jobtracker.jsp) it displays,

               Cluster Summary (Heap Size is 15.5 MB / 1.89 GB)

   What exactly do these figures mean ?

   I know that the second figure (1.89 GB) is determined by the value of 
   the HADOOP_HEAPSIZE variable set in  'conf/'. What I'm not 
   sure about is exactly what it means, or where the first value (15.5 MB) is determined
   or what it means.

   I'm guessing the 1.89 GB is the amount of heap-memory allocated to Hadoop
   on each machine in the cluster. (Correct ?)

   I have no idea what the 15.5 MB means or where it comes from. It never changes,
   not even when a job is running, and I can't find any explanation in the documentation.

   This page,, seems to suggest
   that the 15.5 MB should be the amount of heap memory currently in use but since
   this value never changes - not even when a job is running and I refresh the page 
   - I'm not convinced this is working.   

   I'm asking this question because I have a Mahout job which slowly comes to halt with
   a lot of 'OutOfMemoryError: Java heap space' errors, before it is 'Killed'.

   I'm using Hadoop 0.20.2 and the latest Mahout snapshot version.

   Thanks for any help.


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