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From "Zheng Shao (JIRA)" <>
Subject [jira] Updated: (HIVE-1118) Hive merge map files should have different bytes/mapper setting
Date Mon, 01 Feb 2010 22:10:18 GMT


Zheng Shao updated HIVE-1118:

    Attachment: HIVE-1118.2.patch

The change is trivial, but hopefully it helps our users to use this feature without the concern
of making the job running much longer.

> Hive merge map files should have different bytes/mapper setting
> ---------------------------------------------------------------
>                 Key: HIVE-1118
>                 URL:
>             Project: Hadoop Hive
>          Issue Type: Improvement
>            Reporter: Zheng Shao
>            Assignee: Zheng Shao
>         Attachments: HIVE-1118.1.patch, HIVE-1118.2.patch
> Currently, by default, we get one reducer for each 1GB of input data.
> It's also true for the conditional merge job that will run if the average file size is
smaller than a threshold.
> This actually makes those job very slow, because each reducer needs to consume 1GB of
> Alternatively, we can just use that threshold to determine the number of reducers per
job (or introduce a new parameter).
> Let's say the threshold is 1MB, then we only start the the merge job if the average file
size is less than 1MB, and the eventual result file size will be around 1MB (or another small
> This will remove the extreme cases where we have thousands of empty files, but still
make normal jobs fast enough.

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