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https://issues.apache.org/jira/browse/HIVE-20330?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Adam Szita reassigned HIVE-20330:
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> HCatLoader cannot handle multiple InputJobInfo objects for a job with
> multiple inputs
> -------------------------------------------------------------------------------------
>
> Key: HIVE-20330
> URL: https://issues.apache.org/jira/browse/HIVE-20330
> Project: Hive
> Issue Type: Bug
> Components: HCatalog
> Reporter: Adam Szita
> Assignee: Adam Szita
> Priority: Major
>
> While running performance tests on Pig (0.12 and 0.17) we've observed a huge
> performance drop in a workload that has multiple inputs from HCatLoader.
> The reason is that for a particular MR job with multiple Hive tables as
> input, Pig calls {{setLocation}} on each {{LoaderFunc (HCatLoader)}} instance
> but only one table's information (InputJobInfo instance) gets tracked in the
> JobConf. (This is under config key {{HCatConstants.HCAT_KEY_JOB_INFO}}).
> Any such call overwrites preexisting values, and thus only the last table's
> information will be considered when Pig calls {{getStatistics}} to calculate
> and estimate required reducer count.
> In cases when there are 2 input tables, 256GB and 1MB in size respectively,
> Pig will query the size information from HCat for both of them, but it will
> either see 1MB+1MB=2MB or 256GB+256GB=0.5TB depending on input order in the
> execution plan's DAG.
> It should of course see 256.00097GB in total and use 257 reducers by default
> accordingly.
> In unlucky cases this will be 2MB and 1 reducer will have to struggle with
> 256GB...
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