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https://issues.apache.org/jira/browse/HIVE-18362?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on HIVE-18362 started by wan kun.
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> Introduce a parameter to control the max row number for map join convertion
> ---------------------------------------------------------------------------
>
> Key: HIVE-18362
> URL: https://issues.apache.org/jira/browse/HIVE-18362
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Reporter: wan kun
> Assignee: wan kun
> Priority: Minor
>
> The compression ratio of the Orc compressed file will be very high in some
> cases.
> The test table has three Int columns, with twelve million records, but the
> compressed file size is only 4M. Hive will automatically converts the Join to
> Map join, but this will cause memory overflow. So I think it is better to
> have a parameter to limit to the total number of table records in the Map
> Join convertion, and if the total number of records is larger than that, it
> can not be converted to Map join.
> *hive.auto.convert.join.max.number = 2500000L*
> The default value for this parameter is 2500000, because so many records
> occupy about 700M memory in clint JVM, and 2500000 records for Map Join are
> also large tables.
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