[jira] [Resolved] (CALCITE-3711) Correlate should override estimateRowCount

["Vladimir Sitnikov (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-3711?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Sitnikov resolved CALCITE-3711.
----------------------------------------
    Fix Version/s: 1.22.0
       Resolution: Fixed

Fixed in https://github.com/apache/calcite/commit/9db466ddb26c472411bc4ce27bf62391381912cb

> Correlate should override estimateRowCount
> ------------------------------------------
>
>                 Key: CALCITE-3711
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3711
>             Project: Calcite
>          Issue Type: Improvement
>    Affects Versions: 1.21.0
>            Reporter: Ruben Q L
>            Assignee: Vladimir Sitnikov
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.22.0
>
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> Currently, Correlate inherits the {{estimateRowCount}} implementation from AbstractRelNode:
> {code:java}
> public double estimateRowCount(RelMetadataQuery mq) {
>   return 1.0;
> }
> {code}
> which gives a "default" (but unrealistic) row count computation.
> This has several issues:
> - This value may be used by {{Correlate#computeSelfCost}} (and by inheritance by LogicalCorrelate / EnumerableCorrelate):
> {code:java}
> @Override public RelOptCost computeSelfCost(final RelOptPlanner planner, final RelMetadataQuery mq) {
>   double rowCount = mq.getRowCount(this);  // by default: estimateRowCount, i.e. 1.0
>   ...
> {code}
> - As the current state, this value will definitely by used by several join algorithms in their cost computation if their left/right child is a Correlate:
> {code:java}
> public class EnumerableHashJoin extends Join implements EnumerableRel {
> ...
>   @Override public RelOptCost computeSelfCost(RelOptPlanner planner, RelMetadataQuery mq) {
>     ...
>     final double rightRowCount = right.estimateRowCount(mq); // 1.0 if right is a Correlate
>     final double leftRowCount = left.estimateRowCount(mq); // 1.0 if left is a Correlate
>     ... 
> {code}
> Even though cost computation is pluggable (which would help solving issues like the first one, but not issues like the second one), IMHO we should provide a more realistic default {{Correlate#estimateRowCount}} computation.



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