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https://issues.apache.org/jira/browse/PIG-3241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13599097#comment-13599097
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Rohini Palaniswamy commented on PIG-3241:
-----------------------------------------
I was wrong about iterator.remove() of HashMap throwing
ConcurrentModificationException. Happens only while iterating directly over the
entrySet()
{code}
for (Entry<String, String> entry : map.entrySet()) {
map.remove(entry.getKey());
}
{code}
throws ConcurrentModificationException
{code}
Iterator<Entry<String, String>> spillingIterator = map.entrySet().iterator();
Entry<String, String> entry = spillingIterator.next();
spillingIterator.remove();
{code}
does not throw ConcurrentModificationException
So theoretically it should be fine if the map was accessed within a single
thread. Need to investigate if there is more than one thread accessing
POPartialAgg. Possible that it could be a 2.0 issue. Simple fix would be to
change that to ConcurrentHashMap, but need to find the underlying cause to
assess further impact. I am blocked with few deadlines before going on vacation
and don't have time to spare for the investigation. I am fine if anyone else
can take a look at this. Cheolsoo?
[~lohit],
Can you change it to ConcurrentHashMap and compile and see that fixes the
problem for you?
> ConcurrentModificationException in POPartialAgg
> -----------------------------------------------
>
> Key: PIG-3241
> URL: https://issues.apache.org/jira/browse/PIG-3241
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.11
> Reporter: Lohit Vijayarenu
> Priority: Blocker
> Fix For: 0.12, 0.11.1
>
>
> While running few PIG scripts against Hadoop 2.0, I see consistently see
> ConcurrentModificationException
> {noformat}
> at java.util.HashMap$HashIterator.remove(HashMap.java:811)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POPartialAgg.aggregate(POPartialAgg.java:365)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POPartialAgg.aggregateSecondLevel(POPartialAgg.java:379)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POPartialAgg.getNext(POPartialAgg.java:203)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.processInput(PhysicalOperator.java:308)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POLocalRearrange.getNext(POLocalRearrange.java:263)
> at
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.runPipeline(PigGenericMapBase.java:283)
> at
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:278)
> at
> org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:64)
> at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
> at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:729)
> at org.apache.hadoop.mapred.MapTask.run(MapTask.java:334)
> at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:158)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:396)
> at
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1441)
> at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:153)
> {noformat}
> It looks like there is rawInputMap is being modified while elements are
> removed from it.
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