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From "Jesus Camacho Rodriguez (JIRA)" <j...@apache.org>
Subject [jira] [Work started] (HIVE-20382) Materialized views: Introduce heuristic to favour incremental rebuild
Date Tue, 14 Aug 2018 05:58:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-20382?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Work on HIVE-20382 started by Jesus Camacho Rodriguez.
------------------------------------------------------
> Materialized views: Introduce heuristic to favour incremental rebuild
> ---------------------------------------------------------------------
>
>                 Key: HIVE-20382
>                 URL: https://issues.apache.org/jira/browse/HIVE-20382
>             Project: Hive
>          Issue Type: Improvement
>          Components: Materialized views
>            Reporter: Jesus Camacho Rodriguez
>            Assignee: Jesus Camacho Rodriguez
>            Priority: Major
>         Attachments: HIVE-20382.patch
>
>
> Currently, we do not expose stats over ROW__ID.writeId to the optimizer (this should
be fixed by HIVE-20313). Even if we did, we always assume uniform distribution of the column
values, which can easily lead to overestimations on the number of rows read when we filter
on ROW__ID.writeId for materialized views (think about a large transaction for MV creation
and then small ones for incremental maintenance). This overestimation can lead to incremental
view maintenance not being triggered as cost of the incremental plan is overestimated (we
think we will read more rows than we actually do). This could be fixed by introducing histograms
that reflect better the column values distribution.
> Till both fixes are implemented, we will use a config variable that will multiply the
estimated cost of the rebuild plan and hence will be able to favour incremental rebuild over
full rebuild.



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