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  1. Calcite
  2. CALCITE-3711

Correlate should override estimateRowCount

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: 1.21.0
    • Fix Version/s: 1.22.0
    • Component/s: None

      Description

      Currently, Correlate inherits the estimateRowCount implementation from AbstractRelNode:

      public double estimateRowCount(RelMetadataQuery mq) {
        return 1.0;
      }
      

      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):
        @Override public RelOptCost computeSelfCost(final RelOptPlanner planner, final RelMetadataQuery mq) {
          double rowCount = mq.getRowCount(this);  // by default: estimateRowCount, i.e. 1.0
          ...
        
      • 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:
        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
            ... 
        

      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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              • Assignee:
                vladimirsitnikov Vladimir Sitnikov
                Reporter:
                rubenql Ruben Q L
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