hadoop-mapreduce-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Li Li <fancye...@gmail.com>
Subject Re: how to solve reducer memory problem?
Date Thu, 03 Apr 2014 09:53:57 GMT
 you can think of each TrainingWeights as a very large double[] whose
length is about 10,000,000
TrainingWeights result=null;
int total=0;
for(TrainingWeights weights:values){
if(result==null){
result=weights;
}else{
addWeights(result, weights);
}
total++;
}
if(total>1){
divideWeights(result, total);
}
context.write(NullWritable.get(), result);


On Thu, Apr 3, 2014 at 5:49 PM, Gordon Wang <gwang@gopivotal.com> wrote:

> 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
>

Mime
View raw message