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https://issues.apache.org/jira/browse/HIVE-20332?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jesus Camacho Rodriguez updated HIVE-20332:
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Status: Patch Available (was: In Progress)
> Materialized views: Introduce heuristic on selectivity over ROW__ID to favour
> incremental rebuild
> -------------------------------------------------------------------------------------------------
>
> Key: HIVE-20332
> URL: https://issues.apache.org/jira/browse/HIVE-20332
> Project: Hive
> Issue Type: Improvement
> Components: Materialized views
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Priority: Major
> Attachments: HIVE-20332.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 set
> the selectivity for filter condition on {{ROW\_\_ID}} during the cost
> calculation. Setting that variable to a low value will favour incremental
> rebuild over full rebuild.
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