load a serialized object in hadoop

[Shi Yu]

Hi,

I want to load a serialized HashMap object in hadoop. The file of stored 
object is 200M. I could read that object efficiently in JAVA by setting 
-Xmx as 1000M.  However, in hadoop I could never load it into memory. 
The code is very simple (just read the ObjectInputStream) and there is 
yet no map/reduce implemented.  I set the  
mapred.child.java.opts=-Xmx3000M, still get the 
"java.lang.OutOfMemoryError: Java heap space"  Could anyone explain a 
little bit how memory is allocate to JVM in hadoop. Why hadoop takes up 
so much memory?  If a program requires 1G memory on a single node, how 
much memory it requires (generally) in Hadoop?

Thanks.

Shi

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