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From "Ning Zhang (JIRA)" <>
Subject [jira] Updated: (HIVE-963) no out of memory errors for skewed join
Date Wed, 16 Dec 2009 05:52:18 GMT


Ning Zhang updated HIVE-963:

    Attachment: HIVE-963.patch

Uploading patch HIVE-963.patch. This patch include:

1) Introducing a new class ArrayListWrapper that implements a simple persistent ArrayList
interface (subset). It tries to solve two issues: OutOfMemoryException and data loading and
iteration performance. It only supports add() and a fast iterator iterface through fist()
and next(). So no Iterator class is created. Preliminary experiments shows a 10x faster in
data load. 
2) Changed MapJoinOperator, CommonJoinOperator to use ArrayListWrapper.
3) add a new unit test TestArrayListWrapper.
4) misc. simple factoring and code cleanup in HashMapWrapper.

> no out of memory errors for skewed join
> ---------------------------------------
>                 Key: HIVE-963
>                 URL:
>             Project: Hadoop Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Ning Zhang
>         Attachments: HIVE-963.patch
> Currently, in case of skew, hive runs out of memory.
> A simpler fix would be to use JDBM to store data and use that.
> It can be configurable and JDBM should only be triggered if the number of values for
a given key exceed a given number.

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