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https://issues.apache.org/jira/browse/CALCITE-5314?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated CALCITE-5314:
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Labels: pull-request-available (was: )
> Prune empty parts of a query by exploiting stats/metadata
> ---------------------------------------------------------
>
> Key: CALCITE-5314
> URL: https://issues.apache.org/jira/browse/CALCITE-5314
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Stamatis Zampetakis
> Assignee: Hanumath Rao Maduri
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Currently there is a collection of rules (i.e.,
> [PruneEmptyRules|https://github.com/apache/calcite/blob/4ef9ffe0d4afb80fe95e66d4d9c9e6f5939f70a8/core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java])
> which remove sections of a query plan when it does not produce any rows.
> At the moment, the removal requires an empty {{Values}} operator to be in the
> plan in order to take effect. However, there are cases where queries involve
> empty relations/tables and in that case we could remove parts of the plan as
> well.
> The information if a relation is empty or not can be derived from metadata.
> For example, we could check if the
> [RelMdMaxRowCount|https://github.com/apache/calcite/blob/4ef9ffe0d4afb80fe95e66d4d9c9e6f5939f70a8/core/src/main/java/org/apache/calcite/rel/metadata/RelMdMaxRowCount.java]
> returns zero to derive that the relation is empty.
> Implementation wise there are various alternatives to consider:
> * modify the existing PruneEmptyRule to consider metadata;
> * add new pruning rules relying exclusively on metadata;
> * add new rules checking metadata and turning the empty relation to an empty
> {{Values}} which can then be handled by existing rules
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