Jesus Camacho Rodriguez created HIVE-20332: ----------------------------------------------
Summary: 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 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)