Ruben Q L created CALCITE-3711:
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Summary: 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
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 (i.e. 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
Correlate
final double leftRowCount = left.estimateRowCount(mq); // 1.0 if left is
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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