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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3884) Hive native scan has lower parallelization leading to performance degradation
Date Fri, 02 Oct 2015 00:31:26 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940638#comment-14940638
] 

ASF GitHub Bot commented on DRILL-3884:
---------------------------------------

Github user amansinha100 commented on the pull request:

    https://github.com/apache/drill/pull/185#issuecomment-144884113
  
    +1 LGTM. 


> Hive native scan has lower parallelization leading to performance degradation
> -----------------------------------------------------------------------------
>
>                 Key: DRILL-3884
>                 URL: https://issues.apache.org/jira/browse/DRILL-3884
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization, Storage - Hive
>    Affects Versions: 1.2.0
>            Reporter: Venki Korukanti
>            Assignee: Venki Korukanti
>            Priority: Critical
>             Fix For: 1.2.0
>
>
> Currently {{HiveDrillNativeParquetScan.getScanStats()}} divides the rowCount got from
{{HiveScan}} by a factor and returns that as cost. Problem is all cost calculations and parallelization
depends on the rowCount. Value {{cpuCost}} is not taken into consideration in current cost
calculations in {{ScanPrel}}. In order for the planner to choose {{HiveDrillNativeParquetScan}}
over {{HiveScan}}, rowCount has to be lowered for the former, but this leads to lower parallelization
and performance degradation.
> Temporary fix for Drill 1.2 before DRILL-3856 fully resolves considering CPU cost in
cost model:
> 1. Change ScanPrel to consider the CPU cost in given Stats from GroupScan
> 2. Have higher CPU cost for {{HiveScan}} (SerDe route)
> 3. Lower CPU cost for {{HiveDrillNativeParquetScan}}



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