Check if you can filter non-nulls. That might help. Sent from my iPhone
On Feb 22, 2011, at 12:46 AM, Bennie Schut <bsc...@ebuddy.com> wrote: > I've just set the "hive.exec.reducers.bytes.per.reducer" to as low as 100k > which caused this job to run with 999 reducers. I still have 5 tasks failing > with an outofmemory. > > We have jvm reuse set to 8 but dropping it to 1 seems to greatly reduce this > problem: > set mapred.job.reuse.jvm.num.tasks = 1; > > It's still puzzling me how it can run out of memory. It seems like some of > the reducers get an unequally large share of the work. > > > On 02/18/2011 10:53 AM, Bennie Schut wrote: >> When we try to join two large tables some of the reducers stop with an >> OutOfMemory exception. >> >> Error: java.lang.OutOfMemoryError: Java heap space >> at >> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.shuffleInMemory(ReduceTask.java:1508) >> >> at >> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.getMapOutput(ReduceTask.java:1408) >> >> at >> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.copyOutput(ReduceTask.java:1261) >> >> at >> org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.run(ReduceTask.java:1195) >> >> >> >> When looking at garbage collection for these reduce tasks it's >> continually doing garbage collections. >> Like this: >> 2011-02-17T14:36:08.295+0100: 1250.547: [Full GC [PSYoungGen: >> 111055K->53659K(233024K)] [ParOldGen: 698410K->698410K(699072K)] >> 809466K->752070K(932096K) [PSPermGen: 14450K->14450K(21248K)], 0.1496600 >> secs] [Times: user=1.08 sys=0.00, real=0.15 secs] >> 2011-02-17T14:36:08.600+0100: 1250.851: [Full GC [PSYoungGen: >> 111057K->53660K(233024K)] [ParOldGen: 698410K->698410K(699072K)] >> 809468K->752070K(932096K) [PSPermGen: 14450K->14450K(21248K)], 0.1360010 >> secs] [Times: user=1.00 sys=0.01, real=0.13 secs] >> 2011-02-17T14:36:08.915+0100: 1251.167: [Full GC [PSYoungGen: >> 111058K->53659K(233024K)] [ParOldGen: 698410K->698410K(699072K)] >> 809468K->752070K(932096K) [PSPermGen: 14450K->14450K(21248K)], 0.1325960 >> secs] [Times: user=0.94 sys=0.00, real=0.14 secs] >> 2011-02-17T14:36:09.205+0100: 1251.457: [Full GC [PSYoungGen: >> 111055K->53659K(233024K)] [ParOldGen: 698410K->698410K(699072K)] >> 809466K->752070K(932096K) [PSPermGen: 14450K->14450K(21248K)], 0.1301610 >> secs] [Times: user=0.99 sys=0.00, real=0.13 secs] >> >> >> “mapred.child.java.opts” set to “-Xmx1024M -XX:+UseCompressedOops >> -XX:+UseParallelOldGC -XX:+UseNUMA -Djava.net.preferIPv4Stack=true >> -verbose:gc -XX:+PrintGCDateStamps -XX:+PrintGCDetails >> -Xloggc:/opt/hadoop/logs/task_@tas...@.gc.log” >> >> I've been reducing this parameter “hive.exec.reducers.bytes.per.reducer” >> to as low as 200M but I still get the OutOfMemory errors. I would have >> expected this would drop the amount of data send to the reducers and >> thus not have the OutOfMemory errors to happen. >> >> Any idea's on why this happens? >> >> I'm using a trunk build from around 2011-02-03 >
