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Hadoop, mail # user - mapred.child.ulimit default value of null?

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mapred.child.ulimit default value of null?
Keith Wiley 2011-01-21, 18:02
What is the interpretation of a default value for mapred.child.ulimit of null?  Does that mean children are completely unlimited in their permission to use memory?

If I want to insure maximum memory availability to children, should I leave this null (on a cluster where that is the default), or should I set it to some fairly large number, say 8 GBs (bearing in mind that the parameter's units are KB)?  Is null better given my desire here?

Also, what is a "child" in the context of this question (what does this parameter apply to)?  For example, is a map task itself considered a "child" of the overall job or does this parameter not affect the map task itself but only child processes spawned *by* the map task?

In particular, how would this parameter (or any other relevant parameters you can think of, say, mapred.child.java.opts) affect the availability of memory to compiled C++ code (.so files in the distributed cache) called from a map task via JNI?

What I really want to do is insure that the native routines (C++ .so) called via JNI from a (Java) mapper have maximum memory availability/access on the node.  Ostensibly, the native routines would be permitted to use the entire memory available on the machine.

Thank you.

Keith Wiley               [EMAIL PROTECTED]               www.keithwiley.com

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