2g
On Thu, Apr 3, 2014 at 1:30 PM, Stanley Shi <[email protected]> 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 <[email protected]> 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. >> > >
