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https://issues.apache.org/jira/browse/HIVE-1139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12879442#action_12879442
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Ning Zhang commented on HIVE-1139:
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Sounds good.
> GroupByOperator sometimes throws OutOfMemory error when there are too many
> distinct keys
> ----------------------------------------------------------------------------------------
>
> Key: HIVE-1139
> URL: https://issues.apache.org/jira/browse/HIVE-1139
> Project: Hadoop Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.5.0
> Reporter: Ning Zhang
> Assignee: Arvind Prabhakar
> Attachments: PersistentMap.zip
>
>
> 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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