[jira] [Updated] (HIVE-20382) Materialized views: Introduce heuristic to favour incremental rebuild

["Jesus Camacho Rodriguez (JIRA)" <ji...@apache.org>]

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

Jesus Camacho Rodriguez updated HIVE-20382:
-------------------------------------------
    Attachment: HIVE-20382.01.patch

> 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-20382.01.patch, HIVE-20382.patch, 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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