Q:

org.apache.hadoop.mapred.TaskTracker: Error running child : java.lang.OutOfMemoryError: Java heap space

I am running a simple join query 
select count(*) from t1 join t2 on t1.sno=t2.sno

However it's giving an out of memory exception. 
Both t1 and t2 are in rcfile format clustered and sorted on ssn and have 20 million records each. I have 3 data nodes with 4 GB ram and 2 CPU cores. 
I have tried running a map join but its also failing.
The other configuration options are:
io.sort.mb- 500 MB
io.sort.factor- 10
fs.memory.size.mb- 500 MB

Please advise.

A:

You have to configure the property mapred.child.java.opts, as showed at this post

