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From James Hammerton <james.hammer...@mendeley.com>
Subject Mappers crashing due to running out of heap space during initialisation
Date Tue, 26 Apr 2011 17:55:06 GMT
Hi,

I have a job that runs fine with a small data set in pseudo-distributed mode
on my desktop workstation but when I run it on our Hadoop cluster it falls
over, crashing during the initialisation of some of the mappers. The errors
look like this:

2011-04-26 14:34:04,494 FATAL org.apache.hadoop.mapred.TaskTracker:
Error running child : java.lang.OutOfMemoryError: Java heap space
	at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.<init>(MapTask.java:743)
	at org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:487)
	at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:575)
	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:305)
	at org.apache.hadoop.mapred.Child.main(Child.java:170)


The mapper itself buffers only the previous input and the objects are small
(max 201K in size, most under 50k), so I don't know why this is happening.

What exactly is happening in the area of code referred to in the stack
trace?

Cheers,

James

-- 
James Hammerton | Senior Data Mining Engineer
www.mendeley.com/profiles/james-hammerton

Mendeley Limited | London, UK | www.mendeley.com
Registered in England and Wales | Company Number 6419015

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