*mapred.child.java.opts=-Xmx2g*
On Thu, Apr 3, 2014 at 5:10 PM, Li Li <[email protected]> wrote: > 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. >>> >> >> >
