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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HIVE-1139) GroupByOperator sometimes throws OutOfMemory error when there are too many distinct keys
Date Mon, 08 Feb 2010 19:59:28 GMT
GroupByOperator sometimes throws OutOfMemory error when there are too many distinct keys
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                 Key: HIVE-1139
                 URL: https://issues.apache.org/jira/browse/HIVE-1139
             Project: Hadoop Hive
          Issue Type: Bug
            Reporter: Ning Zhang
            Assignee: Ning Zhang


When a partial aggregation performed on a mapper, a HashMap is created to keep all distinct
keys in main memory. This could leads to OOM exception when there are too many distinct keys
for a particular mapper. A workaround is to set the map split size smaller so that each mapper
takes less number of rows. A better solution is to use the persistent HashMapWrapper (currently
used in CommonJoinOperator) to spill overflow rows to disk. 

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