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https://issues.apache.org/jira/browse/HIVE-1118?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zheng Shao updated HIVE-1118:
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Summary: Add hive.merge.size.per.task to HiveConf (was: Hive merge map
files should have different bytes/mapper setting)
> Add hive.merge.size.per.task to HiveConf
> ----------------------------------------
>
> Key: HIVE-1118
> URL: https://issues.apache.org/jira/browse/HIVE-1118
> Project: Hadoop Hive
> Issue Type: Improvement
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Attachments: HIVE-1118.1.patch, HIVE-1118.2.patch, HIVE-1118.3.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 data.
> 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 number).
> This will remove the extreme cases where we have thousands of empty files,
> but still make normal jobs fast enough.
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