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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 updated HIVE-20330:
------------------------------
    Attachment: HIVE-20330.6.patch

> 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
>         Attachments: HIVE-20330.0.patch, HIVE-20330.1.patch, 
> HIVE-20330.2.patch, HIVE-20330.3.patch, HIVE-20330.4.patch, 
> HIVE-20330.5.patch, HIVE-20330.6.patch
>
>
> 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 seen as 2MB and 1 reducer will have to struggle 
> with the actual 256.00097GB...



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