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From Gordon Wang <gw...@gopivotal.com>
Subject Re: how to solve reducer memory problem?
Date Thu, 03 Apr 2014 09:49:05 GMT
What is the work in reducer ?
Do you have any memory intensive work in reducer(eg. cache a lot of data in
memory) ? I guess the OOM error comes from your code in reducer.


On Thu, Apr 3, 2014 at 5:10 PM, Li Li <fancyerii@gmail.com> wrote:

> *mapred.child.java.opts=-Xmx2g*
>
>
> On Thu, Apr 3, 2014 at 5:10 PM, Li Li <fancyerii@gmail.com> wrote:
>
>> 2g
>>
>>
>> On Thu, Apr 3, 2014 at 1:30 PM, Stanley Shi <sshi@gopivotal.com> wrote:
>>
>>> This doesn't seem like related with the data size.
>>>
>>> How much memory do you use for the reducer?
>>>
>>> Regards,
>>> *Stanley Shi,*
>>>
>>>
>>>
>>> On Thu, Apr 3, 2014 at 8:04 AM, Li Li <fancyerii@gmail.com> wrote:
>>>
>>>> I have a map reduce program that do some matrix operations. in the
>>>> reducer, it will average many large matrix(each matrix takes up
>>>> 400+MB(said by Map output bytes). so if there 50 matrix to a reducer,
>>>> then the total memory usage is 20GB. so the reduce task got exception:
>>>>
>>>> FATAL org.apache.hadoop.mapred.Child: Error running child :
>>>> java.lang.OutOfMemoryError: Java heap space
>>>> at org.apache.hadoop.mapred.IFile$Reader.readNextBlock(IFile.java:344)
>>>> at org.apache.hadoop.mapred.IFile$Reader.next(IFile.java:406)
>>>> at org.apache.hadoop.mapred.Merger$Segment.next(Merger.java:238)
>>>> at org.apache.hadoop.mapred.Merger$MergeQueue.merge(Merger.java:438)
>>>> at org.apache.hadoop.mapred.Merger.merge(Merger.java:142)
>>>> at
>>>> org.apache.hadoop.mapred.ReduceTask$ReduceCopier.createKVIterator(ReduceTask.java:2539)
>>>> at
>>>> org.apache.hadoop.mapred.ReduceTask$ReduceCopier.access$400(ReduceTask.java:661)
>>>> at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:399)
>>>> at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
>>>> at java.security.AccessController.doPrivileged(Native Method)
>>>> at javax.security.auth.Subject.doAs(Subject.java:415)
>>>> at
>>>> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)
>>>> at org.apache.hadoop.mapred.Child.main(Child.java:249)
>>>>
>>>> one method I can come up with is use Combiner to save sums of some
>>>> matrixs and their count
>>>> but it still can solve the problem because the combiner is not fully
>>>> controled by me.
>>>>
>>>
>>>
>>
>


-- 
Regards
Gordon Wang

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