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From "Qiaoyi Ding (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-1139) GroupByOperator sometimes throws OutOfMemory error when there are too many distinct keys
Date Tue, 31 Jul 2018 04:47:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16563143#comment-16563143
] 

Qiaoyi Ding commented on HIVE-1139:
-----------------------------------

Hi all, I'm new to HIVE, and i find there is no spilling when hash agg having lots of entriesĀ in
the hash map which couldĀ cause OOM.

So, is this issue still a open, or any update?

> 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: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.5.0
>            Reporter: Ning Zhang
>            Assignee: Arvind Prabhakar
>            Priority: Major
>         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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