I have suddenly began to get this error (hadoop error code 2) even for not-so-big queries. I am running a 6 node cluster. I tried to run the queries with 6 and 10 reducers but got the same result.
On Wed, Feb 23, 2011 at 8:25 PM, Bennie Schut <bsc...@ebuddy.com> wrote: > We filter nulls already before the tables are filled but then this will > probably cause a skew in the keys like Paul was saying. I'm running some > queries on the keys to see if that's the case. > I do expect there will be large differences in distribution of some of the > keys. > I'm looking at "set hive.optimize.skewjoin=true" before the query to see if > that helps. Will try that later. > > > On 02/23/2011 05:25 AM, Mapred Learn wrote: > >> Oops I meant nulls. >> >> Sent from my iPhone >> >> On Feb 22, 2011, at 8:22 PM, Mapred Learn<mapred.le...@gmail.com> wrote: >> >> 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 >>>>> >>>> >
