[ https://issues.apache.org/jira/browse/HIVE-20332?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Jesus Camacho Rodriguez reassigned HIVE-20332: ---------------------------------------------- > 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 > > Currently, we do not expose stats over {{ROW__ID.writeId}} to the optimizer. > 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 that moment, 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. -- This message was sent by Atlassian JIRA (v7.6.3#76005)