The UDAF works great for lower cardinality and integer numbers but as soon as i run it on billions of rows with bigint i run into the following error.

java.lang.Exception: java.lang.OutOfMemoryError: Java heap space
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:404)
Caused by: java.lang.OutOfMemoryError: Java heap space
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.init(MapTask.java:826)
at org.apache.hadoop.mapred.MapTask.createSortingCollector(MapTask.java:376)
at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:406)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:332)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)

I did set mapred.child.java.opts=-Xmx8000m and it still fails. I am wondering if there is a memory leak issue or something. Is there a way to debug the UDAF?